Cellulose acylate film, its production method, polarizer and liquid crystal display device

ABSTRACT

A cellulose acylate film containing a cellulose acylate and a sugar ester compound having from 1 to 12 pyranose structures or furanose structures in which at least one hydroxyl group is esterified, the film satisfying 40 nm≦Re(550)≦60 nm and 100 nm≦Rth(550)≦140 nm, and having a dimensional change of −0.5 to 0.5% and an internal haze of at most 0.1%.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority from JapanesePatent Application No. 2010-96470, filed on Apr. 19, 2010; JapanesePatent Application No. 2010-188438, filed on Aug. 25, 2010; and JapanesePatent Application No. 2011-51796, filed on Match 9, 2011, the contentsof which are herein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cellulose acylate film and itsproduction method, and to a polarizer and a liquid crystal displaydevice comprising the cellulose acylate film. In particular, theinvention relates to a cellulose acylate film favorable for use as anoptical film such as a polarizer protective film, an opticalcompensatory film, etc.

2. Description of the Related Art

With the recent tendency toward advancing TV use of liquid crystaldisplay devices, the panel size of the devices is enlarged andhigh-definition and low-price liquid crystal display devices are muchdesired. In particular, VA-mode liquid crystal display devices have arelatively high contrast and enjoy a relatively high production yield,and are therefore most popular liquid crystal display devices for TVuse.

However, VA-mode liquid crystal display devices have a problem in that,at the time of black state, the devices could provide black that is goodin some degree in the normal direction to the display panel, but whenthe black state panel is seen in viewing angle directions (obliquedirections), there occurs light leakage to disable background blackdisplay whereby the viewing angle is narrowed. Accordingly, aretardation film is desired capable of expressing a retardation level insuch a degree that enables viewing angle compensation.

Recently, further, for preventing the neutral tone on a liquid crystaldisplay panel from being yellowed, a multigap (MG) cell has become usedin which the thickness of the liquid crystal layer, or that is, the cellgap is changed for every color. However, the multigap cell isproblematic in that, as compared with that on a conventional liquidcrystal display panel, the color shift at the time of black state inviewing angle directions increases, and therefore, it has become muchdesired to further improve the multigap cell in point of preventing thecolor shift at the time of black state in viewing angle directions on aliquid crystal display panel.

On the other hand, the demand for use of liquid crystal display devicesin various environments has become increased, and in particular, thedemand for favorable use thereof in high temperature and high humidityenvironments, for example, for outdoor use thereof has increased. Incase where a retardation film of which the dimensional change in use inhigh temperature and high humidity environments is large is incorporatedin a liquid crystal display device, there may occur corner unevenness onthe liquid crystal display panel, and therefore, it is desired toimprove the durability of the film in high temperature and high humidityenvironments.

Further improvement of the display performance of liquid crystal displaydevices and further reduction in the production cost thereof are stilldesired, and it is desired to provide an inexpensive retardation filmcapable of fully attaining viewing angle compensation even though it isthin, and capable of enabling further contrast increase.

Regarding the requirements, it is known that use of a retardation filmhaving reversed wavelength dispersion characteristics of retardation, orthat is, a retardation film having optical properties of such that itsin-plane retardation Re increases on a longer wavelength side iseffective for preventing color shift at the time of black state inviewing angle directions on a liquid crystal display panel (see JP-A2009-1696).

Films having reversed wavelength dispersion characteristics ofretardation that have heretofore been investigated are produced byadding an additive having a negative intrinsic birefringence to a resinfilm. However, the additive having a negative intrinsic birefringence isexpensive and has some problems in that, when such an additive having anegative intrinsic birefringence is added to a resin film, then thethickness-direction retardation Rth of the film lowers and therefore, inorder to make the film express a desired retardation level, thethickness of the film must be increased or the amount of the retardationenhancer to be added to the film must be increased, and as a result,from the viewpoint of the material cost, the additive is unsatisfactory.

As opposed to this, JP-A 2009-1696 discloses a technique of adding anacrylic polymer having a negative intrinsic birefringence and further asugar ester compound to a phthalyl/acetyl-modified heterogeneouscellulose-mixed cellulose acylate, thereby improving the light leakageresistance, the color shift resistance, the front contrast, theretardation and the wavelength dispersion characteristics of retardationof the resulting film. This patent reference suggests the possibility ofstretching the film, but says nothing about high temperature and highhumidity treatments of the film after stretching.

On the other hand, for improving the dimensional stability of films inhigh temperature and high humidity environments, JP-A 2002-179819discloses a method of once drying a formed cellulose ester film followedby humidifying the film to thereby increase the water content of thefilm. The patent reference says that it is preferable to stretch the dryfilm in a film width direction (direction perpendicular to the filmconveying direction) by from 1 to 20% or so at 80 to 150° C. or so,disclosing examples where a film is, after stretched, humidified at 70°C. and at a relative humidity of 80% or in a water bath at 40° C.However, the patent reference says nothing about use of a sugar estercompound.

SUMMARY OF THE INVENTION

The present inventors investigated the film described in JP-A 2009-1696and have known that the properties of the film do not reach the levelrecently required in the art and that the reversed wavelength dispersioncharacteristics of retardation of the film are poor and the internalhaze thereof is large. In addition, the inventors have further knownthat the color shift u′ and v′ in incorporation of the film in a liquidcrystal display device could not be controlled to be on a level of atmost 0.06 recently desired in the art for practical use, and further,the front contrast is also unsatisfactory. In Table 3 in the patentreference, the haze of the film No. 201 (comparative Example) in which asugar ester compound alone is used with no use of a resin having anegative intrinsic birefringence is extremely high; or that is, anexpensive resin having a negative intrinsic birefringence isindispensable in the film and the film is therefore unsatisfactory fromthe viewpoint of the production cost.

Similarly, the inventors investigated the film described in JP-A2002-179819 and have known that the internal haze of the film increasesextremely through humidification and, when the film is incorporated in aliquid crystal display device, then the front contrast of the devicedecreases. The inventors have further found that, in case where acellulose acylate having a degree of acetylation of 61.0% is formed intoa film through humidification under the condition described in examplesin the patent reference, the optical appearance of the film is poor sofar as an expensive retardation enhancer is not added thereto, andtherefore the film is still unsatisfactory from the viewpoint of boththe viewing angle compensation capability and the production costthereof.

An object of the invention is to provide a cellulose acylate film havingthe advantages of high optical appearance, strong reversed wavelengthdispersion characteristics of retardation, small haze, good dimensionalstability in high temperature and high humidity environments and lowproduction cost, and to provide a method for producing the film. Anotherobject is to provide a liquid crystal display device free from problemsof color shift and corner unevenness at the time of black state inviewing angle directions and having the advantages of high contrast bothin front direction and in viewing angle directions.

With the above-mentioned objects, the inventors have assiduously studiedand, as a result, have found that, even though a compound having anegative birefringence is not used but only when an sugar ester is usedas an additive and when a stretched film is processed for hightemperature and high humidity treatment in an environment at a specifictemperature and at a specific volumetric humidity, then surprisingly acellulose acylate film having the advantages of high optical appearance,strong reversed wavelength dispersion characteristics of retardation,small haze, good dimensional stability in high temperature and highhumidity environments and low production cost can be produced.

Specifically, the inventors have found that, when a stretched film isprocessed for high temperature and high humidity treatment under aspecific condition using a specific additive, then the above-mentionedobjects can be attained, and have completed the present invention.

Concretely, the inventors have attained the objects according to thefollowing means:

[1] A cellulose acylate film comprising a cellulose acylate and a sugarester compound wherein:

the sugar ester comprises from 1 to 12 pyranose structures or furanosestructures in which at least one hydroxyl group is esterified,

the film has an in-plane retardation at a wavelength of 550 nmsatisfying the following formula (1):

40 nm≦Re(550)≦60 nm  (1)

wherein Re(550) means the in-plane retardation of the film at awavelength of 550 nm,

the film has a thickness-direction retardation at a wavelength of 550 nmsatisfying the following formula (2):

100 nm≦Rth(550)≦140 nm  (2)

wherein Rth(550) means the thickness-direction retardation of the filmat a wavelength of 550 nm,

the film has a dimensional change before and after 24 hours at 60° C.and at a relative humidity of 90% satisfying the following formula (3)in the film conveying direction and in the direction perpendicularthereto,

−0.5%≦{(L′−L0)/L0}×100≦0.5%  (3)

wherein L0 means the length (unit: mm) of the film before aged for 24hours at 60° C. and at a relative humidity of 90%; and L′ means thelength (unit: mm) of the film after aged for 24 hours at 60° C. and at arelative humidity of 90% and further after conditioned for 2 hours, and

the film has an internal haze of at most 0.1%.

[2] The cellulose acylate film of [1], satisfying the following formula(4):

0.02≦ΔRe/Re(550)≦0.28  (4)

ΔRe=Re(630)−Re(450)  (4′)

wherein Re(630) means the in-plane retardation of the film at awavelength of 630 nm; Re(450) means the in-plane retardation of the filmat a wavelength of 450 nm; Re(550) means the in-plane retardation of thefilm at a wavelength of 550 nm.

[3] The cellulose acylate film of [1], satisfying the following formula(5):

0.11≦ΔRe/Re(550)≦0.23  (5)

ΔRe=Re(630)−Re(450)  (5′)

wherein Re(630) means the in-plane retardation of the film at awavelength of 630 nm; Re(450) means the in-plane retardation of the filmat a wavelength of 450 nm; Re(550) means the in-plane retardation of thefilm at a wavelength of 550 nm.

[4] The cellulose acylate film of any one of [1] to [3], wherein thedegree of acyl substitution of the cellulose acylate is from 2.0 to 2.6.

[5] The cellulose acylate film of any one of [1] to [4], wherein thecellulose acylate is a cellulose acetate.

[6] The cellulose acylate film of any one of [1] to [5], comprising anadditive having a negative intrinsic birefringence.

[7] The cellulose acylate film of any one of [1] to [6], satisfying thefollowing formula (6):

1.5×10⁻³ <Rth(550)/d  (6)

wherein Rth(550) means the thickness-direction retardation (unit: nm) ofthe film at a wavelength of 550 nm, and d means the thickness (unit: mm)of the film.

[8] The cellulose acylate film of any one of [1] to [7], having athickness of from 40 to 80 μm.

[9] The cellulose acylate film of any one of [1] to [8], comprising anitrogen-containing aromatic compound-type plasticizer.

[10] A method for producing a cellulose acylate film, which comprises

forming a polymer solution that comprises a cellulose acylate and asugar ester compound comprising from 1 to 12 pyranose structures orfuranose structures in which at least one hydroxyl group is esterified,into a film,

stretching the film, and

processing the stretched film for high temperature and high humiditytreatment under a condition satisfying the following formulae (7) and(8):

70° C.≦temperature of the treatment≦140° C.  (7)

250 g/m³≦volumetric humidity of the treatment≦400 g/m³  (8)

[11] The method for producing a cellulose acylate film of [10], whereinthe film is stretched at a temperature not higher than (Tg−5° C.) inwhich Tg means the glass transition temperature (unit: ° C.) of theunstretched cellulose acylate film.

[12] The method for producing a cellulose acylate film of [10] or [11],wherein the cellulose acylate has a degree of acyl substitution of from2.0 to 2.6.

[13] The method for producing a cellulose acylate film of any one of[10] to [12], wherein the cellulose acylate is a cellulose acetate.

[14] The method for producing a cellulose acylate film of any one of[10] to [13], wherein the polymer solution comprises an additive havinga negative intrinsic birefringence.

[15] The method for producing a cellulose acylate film of any one of[10] to [14], wherein the polymer solution comprises anitrogen-containing aromatic compound-type plasticizer.

[16] A cellulose acylate film produced by the method for producing acellulose acylate film of any one of [10] to [15].

[17] A polarizer comprising a polarizing element and the celluloseacylate film of any one of [1] to [9] and [15] on at least one side ofthe polarizing element.

[18] A liquid crystal display device comprising at least one polarizerof. [17].

The invention provides a cellulose acylate film having the advantages ofhigh optical appearance, strong reversed wavelength dispersioncharacteristics of retardation, small haze, good dimensional stabilityin high temperature and high humidity environments and low productioncost, and a method for producing the film. In addition, the inventionalso provides a liquid crystal display device free from problems ofcolor shift and corner unevenness at the time of black state in viewingangle directions and having the advantages of high contrast both infront direction and in viewing angle directions.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic cross-sectional view of one example of a VA-modeliquid crystal display device of the invention. In the drawing, 11 is apolarizing element, 12 is a polarizing element, 13 is a liquid crystalcell, 14 and 15 each are a cellulose acylate film.

BEST MODE FOR CARRYING OUT THE INVENTION

The contents of the invention are described in detail hereinunder. Thedescription of the constitutive elements of the invention givenhereinunder is for some typical embodiments of the invention, to which,however, the invention should not be limited. In this description, thenumerical range expressed by the wording “a number to another number”means the range that falls between the former number indicating thelowermost limit of the range and the latter number indicating theuppermost limit thereof. In this description, “front side” means thepanel side of the display device, and “rear side” means the backlightside thereof. In this description, “front” means the normal direction tothe panel of the display device, and “front contrast (hereinafter“contrast” may be referred to as CR)” means the contrast as computedfrom the brightness at the time of white state and the brightness at thetime of black state measured in the normal direction to the displaypanel.

[Cellulose Acylate Film]

The cellulose acylate film of the invention (hereinafter this may bereferred to as “the film of the invention”) comprises a celluloseacylate and a sugar ester compound containing from 1 to 12 pyranosestructures or furanose structures where at least one hydroxyl group isesterified, of which the in-plane retardation and thethickness-direction retardation at a wavelength of 550 nm satisfy thefollowing formulae (1) and (2), respectively, of which the dimensionalchange before and after 24 hours at 60° C. and at a relative humidity of90% satisfies the following formula (3) in the film conveying directionand in the direction perpendicular thereto, and of which the internalhaze is at most 0.1%:

40 nm≦Re(550)≦60 nm  (1)

wherein Re(550) means the in-plane retardation of the film at awavelength of 550 nm,

100 nm≦Rth(550)≦140 nm  (2)

wherein Rth(550) means the thickness-direction retardation of the filmat a wavelength of 550 nm,

−0.5%≦{(L′−L0)/L0}×100≦0.5%  (3)

wherein L0 means the length (unit: mm) of the film before aged for 24hours at 60° C. and at a relative humidity of 90%; and L′ means thelength (unit: mm) of the film after aged for 24 hours at 60° C. and at arelative humidity of 90% and further after conditioned for 2 hours.

The film of the invention is described below.

<Cellulose Acylate>

The film of the invention contains a cellulose acylate. The celluloseacylate for use in the invention is described below.

The starting cellulose for the cellulose acylate for use in theinvention includes cotton linter and wood pulp (hardwood pulp, softwoodpulp), etc.; and any cellulose acylate obtained from any startingcellulose can be used herein. As the case may be, different startingcelluloses may be mixed for use herein. The starting cellulose materialsare described in detail, for example, in Marusawa & Uda's “PlasticMaterial Lecture (17), Cellulosic Resin” (by Nikkan Kogyo Shinbun,1970), and in Hatsumei Kyokai Disclosure Bulletin No. 2001-1745, pp.7-8. Cellulose materials described in these may be used for thecellulose acylate film for the invention with no specific limitation.

The cellulose acylate preferably used in the invention is described indetail. The β-1,4-bonding glucose unit to constitute cellulose has afree hydroxyl group at the 2-, 3- and 6-positions. The cellulose acylateis a polymer produced by esterifying a part or all of those hydroxylgroups in cellulose with an acyl group. The degree of acyl substitutionmeans the total of the ratio of acylation of the hydroxyl group incellulose positioned in the 2-, 3- and 6-positions in the unit therein.In case where the hydroxyl group is 100% acylated at each position, thedegree of substitution at that position is 1.

Only one or two or more different types of acyl groups may be used,either singly or as combined, in the cellulose acylate for use in theinvention.

Not specifically defined, the acyl group in the cellulose acylate foruse in the invention may be an aliphatic group or an aryl group. Forexample, the ester is an alkylcarbonyl ester, an alkenylcarbonyl ester,an aromatic carbonyl ester or an aromatic alkylcarbonyl ester ofcellulose, in which the acyl group may be further substituted. Preferredexamples of the acyl group include an acetyl group, a propionyl group, abutanoyl group, a heptanoyl group, a hexanoyl group, an octanoyl group,a decanoyl group, a dodecanoyl group, a tridecanoyl group, atetradecanoyl group, a hexadecanoyl group, an octadecanoyl group, aniso-butanoyl group, a tert-butanoyl group, a cyclohexanecarbonyl group,an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoylgroup, etc. Of those, preferred are an acetyl group, a propionyl group,a butanoyl group, a dodecanoyl group, an octadecanoyl group, atert-butanoyl group, an oleoyl group, a benzoyl group, anaphthylcarbonyl group, and a cinnamoyl group; more preferred are anacetyl group, a propionyl group and a butanoyl group (acyl group havingfrom 2 to 4 carbon atoms). Even more preferred is an acetyl group (inthis case, the cellulose acylate is a cellulose acetate).

The cellulose acylate includes triacetyl cellulose (TAC), diacetylcellulose (DAC), cellulose acetate propionate (CAP), cellulose acetatebutyrate (CAB), cellulose acetate phthalate, etc. Preferably, in thecellulose acylate film of the invention, all the acyl groups in thecellulose acylate are acetyl groups from the viewpoint of theretardation and the cost of the film.

Preferably, in the film of the invention, the degree of acylsubstitution of the cellulose acylate satisfies from 2.0 to 2.6 from theviewpoint of the retardation and the cost of the film and from theviewpoint that, when the film is incorporated in a liquid crystaldisplay device, it is effective for increasing the display contrast ofthe device. More preferably, the degree of acyl substitution of thecellulose acylate is from 2.1 to 2.55, even more preferably from 2.20 to2.50

The degree of acyl substitution may be determined according to themethod stipulated in ASTM-D817-96. The part not substituted with an acylgroup is generally a hydroxyl group.

In a preferred embodiment of the invention, even a cellulose acylatefilm that contains a cellulose acylate having a low degree of acylsubstitution could be improved in both the dimensional stability underhigh temperature and high humidity conditions and the reversedwavelength dispersion characteristics of retardation (having positiveΔRe) thereof, and therefore in the invention, a cellulose acylate filmthat contains such a cellulose acylate having a low degree of acylsubstitution can be produced. The cellulose acylate film that containssuch a cellulose acylate having a low degree of acyl substitution couldnot be produced under conventional production conditions owing to poordimensional stability thereof under high temperature and high humidityconditions.

The cellulose acylate can be produced in known methods. For example, itcan be produced according to the method described in JP-A 10-45804.

In case where an acid anhydride or an acid chloride is used as theacylating agent for acylation of cellulose, an organic acid such asacetic acid, or methylene chloride or the like may be used as theorganic solvent to be the reaction solvent.

In case where the acylating agent is an acid anhydride, the catalyst ispreferably a protic catalyst such as sulfuric acid; and in case wherethe acylating agent is an acid chloride (e.g., CH₃CH₂COCl), a basiccompound may be used as the catalyst.

A most popular industrial-scale production method for a mixed fatty acidester of cellulose comprises acylating cellulose with a mixed organicacid component that contains a fatty acid (e.g., acetic acid, propionicacid, valeric acid) corresponding to an acetyl group or other acylgroup, or its acid anhydride.

Preferably, the molecular weight of the cellulose acylate is from 40000to 200000 in terms of the number-average molecular weight (Mn) thereof,more preferably from 100000 to 200000. Also preferably, the ratio ofMw/Mn of the cellulose acylate for use in the invention is at most 4.0,more preferably from 1.4 to 2.3.

In the invention, the mean molecular weight and the molecular weightdistribution of cellulose acylate and others may be determined bymeasuring the number-average molecular weight (Mn) and theweight-average molecular weight (Mw) thereof through gel permeationchromatography (GPC) followed by computing the ratio of the resultingdata according to the method described in WO2008-126535.

<Additive> (Sugar Ester Compound)

The film of the invention contains a sugar ester compound.

Adding a sugar ester compound to the cellulose acylate film may reducethe internal haze of the film even in the presence of high temperatureand high humidity treatment after stretching the film, not detractingfrom the ability of the film to express the optical properties thereof.Further, when the cellulose acylate film of the invention is used in aliquid crystal display device, the front contrast can be significantlyimproved.

Sugar Residue

The sugar ester compound means a compound where at least onesubstitutable compound (for example, hydroxyl group, carboxyl group) inthe monose or polyose constituting the compound is ester-bonded to atleast one substituent therein. Specifically, the sugar ester compound asreferred to herein includes sugar derivatives in a broad sense of theword, and for example, includes compounds having a sugar residue as thestructural unit thereof such as gluconic acid. Concretely, the sugarester compound includes an ester of glucose and a carboxylic acid, andan ester of gluconic acid and an alcohol.

The substitutable group in the monose or polyose constituting the sugarester compound is preferably a hydroxyl group.

The sugar ester compound includes a monose or polyose-derived structure(hereinafter this may be referred to as a sugar residue) thatconstitutes the sugar ester compound. The structure per monose of thesugar residue is referred to as the structural unit of the sugar estercompound. The structural unit of the sugar ester compound preferablyincludes a pyranose structural unit or a furanose structural unit, morepreferably, all the sugar residues are pyranose structural units orfuranose structural units. In case where the sugar ester is formed of apolyose, it preferably includes both a pyranose structural unit and afuranose structural unit.

The sugar residue of the sugar ester compound may be a pentose-derivedone or a hexose-derived one, but is preferably a hexose-derived one.

Preferably, the number of the structural units contained in the sugarester compound is from 1 to 12, more preferably from 1 to 6, even morepreferably 1 or 2.

In the invention, preferably, the sugar ester compound contains from 1to 12 pyranose structural units or furanose structural units in which atleast one hydroxyl group is esterified, even more preferably, one or twopyranose structural units or furanose structural units in which at leastone hydroxyl group is esterified.

Examples of monoses or polyoses containing from 2 to 12 monose unitsinclude, for example, erythrose, threose, ribose, arabinose, xylose,lyxose, arose, altrose, glucose, fructose, mannose, gulose, idose,galactose, talose, trehalose, isotrehalose, neotrehalose, trehalosamine,kojibiose, nigerose, maltose, maltitol, isomaltose, sophorose,laminaribiose, cellobiose, gentiobiose, lactose, lactosamine, lactitol,lactulose, melibiose, primeverose, rutinose, scillabiose, sucrose,sucralose, turanose, vicianose, cellotriose, chacotriose, gentianose,isomaltotriose, isopanose, maltotriose, manninotriose, melezitose,panose, planteose, raffinose, solatriose, umbelliferose, lycotetraose,maltotetraose, stachyose, baltopentaose, belbalcose, maltohexaose,α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin, xylitol,sorbitol, etc.

Preferred are ribose, arabinose, xylose, lyxose, glucose, fructose,mannose, galactose, trehalose, maltose, cellobiose, lactose, sucrose,sucralose, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin,δ-cyclodextrin, xylitol, sorbitol; more preferred are arabinose, xylose,glucose, fructose, mannose, galactose, maltose, cellobiose, sucrose,β-cyclodextrin, γ-cyclodextrin; and even more preferred are xylose,glucose, fructose, mannose, galactose, maltose, cellobiose, sucrose,xylitol, sorbitol. The sugar ester compound has a glucose skeleton or asucrose skeleton, which is described in [0059] in JP-A 2009-1696 as thecompound 5 therein. The sugar ester compound of the type is, as comparedwith the sugar ester compound having a maltose skeleton used in Examplesin the patent reference, especially preferred from the viewpoint of thecompatibility thereof with polymer.

Structure of Substituent

More preferably, the sugar ester compound for use in the invention has,including the substituent therein, a structure represented by thefollowing formula (1):

(OH)_(p)-G-(L¹-R¹¹)_(q)(O—R¹²)_(r)  (1)

wherein G represents a sugar residue; L¹ represents any one of —O—, —CO—or —NR¹³—; R¹¹ represents a hydrogen atom or a monovalent substituent;R¹² represents a monovalent substituent bonding to the formula via anester bond; p, q and r each independently indicate an integer of 0 ormore, and p+q+r is equal to the number of the hydroxyl groups on thepresumption that G is an unsubstituted sugar group having a cyclicacetal structure.

The preferred range of G is the same as the preferred range of theabove-mentioned sugar residue.

L¹ is preferably —O— or —CO—, more preferably —O—. When L¹ is —O—, it ismore preferably an ether bond or ester bond-derived linking group, evenmore preferably an ester bond-derived linking group.

In case where the formula has plural L¹'s, then they may be the same ordifferent.

Preferably, at least one of R¹¹ and R¹² has an aromatic ring.

In particular, in case where L¹ is —O— (or that is, in case where thehydroxyl group in the above-mentioned sugar ester compound issubstituted with R¹¹ and R¹²), preferably, R¹¹, R¹² and R¹³ are selectedfrom a substituted or unsubstituted acyl group, a substituted orunsubstituted aryl group, a substituted or unsubstituted alkyl group, ora substituted or unsubstituted amino group, more preferably from asubstituted or unsubstituted acyl group, a substituted or unsubstitutedalkyl group, or a substituted or unsubstituted aryl group, even morepreferably from an unsubstituted acyl group, a substituted orunsubstituted alkyl group, or an unsubstituted aryl group.

In case where the formula has plural R¹¹'s, R¹²'s and R¹³'s, they may bethe same or different.

p is an integer of 0 or more, and its preferred range is the same as thepreferred range of the number of the hydroxyl groups per the monose unitto be mentioned below, however, in the invention, p is preferably zero(0).

r is preferably a number larger than the number of the pyranosestructural units or the furanose structural units contained in G.

q is preferably 0.

p+q+r is equal to the number of the hydroxyl groups on the presumptionthat G is an unsubstituted sugar group having a cyclic acetal structure,and therefore, the uppermost limit of these p, q and r is specificallydefined depending on the structure of G.

Preferred examples of the substituent of the sugar ester compoundinclude an alkyl group (preferably an alkyl group having from 1 to 22carbon atoms, more preferably from 1 to 12 carbon atoms, even morepreferably from 1 to 8 carbon atoms, for example, a methyl group, anethyl group, a propyl group, a hydroxyethyl group a hydroxypropyl group,a 2-cyanoethyl group, a benzyl group), an aryl group (preferably an arylgroup having from 6 to 24 carbon atoms, more preferably from 6 to 18carbon atoms, even more preferably from 6 to 12 carbon atoms, forexample, a phenyl group, a naphthyl group), an acyl group (preferably anacyl group having from 1 to 22 carbon atoms, more preferably from 2 to12 carbon atoms, even more preferably from 2 to 8 carbon atoms, forexample, an acetyl group, a propionyl group, a butyryl group, apentanoyl group, a hexanoyl group, an octanoyl group, a benzoyl group, atoluoyl group, a phthalyl group), an amide group (preferably an amidegroup having from 1 to 22 carbon atoms, more preferably from 2 to 12carbon atoms, even more preferably from 2 to 8 carbon atoms, forexample, a formamide group, an acetamide group), an imide group(preferably an imide group having from 4 to 22 carbon atoms, morepreferably from 4 to 12 carbon atoms, even more preferably from 4 to 8carbon atoms, for example, a succinimide group, a phthalimide group), anaryl-alkyl group (preferably an aryl group having from 7 to 25 carbonatoms, more preferably from 7 to 19 carbon atoms, even more preferablyfrom 7 to 13 carbon atoms, for example, a benzyl group). Of those, morepreferred are an alkyl group and an acyl group; and even more preferredare a methyl group, an acetyl group, a benzoyl group and a benzyl group;and especially preferred are an acetyl group and a benzyl group.Especially of those, in case where the constitutive sugar in the sugarester compound is a sucrose skeleton, preferred are sugar estercompounds having an acetyl group and a benzyl group as the substituentstherein, as compared with the sugar ester compound with a benzoyl groupdescribed as the compound 3 in [0058] in JP-A 2009-1696 and used inExamples in the patent reference, in point of the compatibility thereofwith polymer.

Preferably, the number of the hydroxyl groups per the structural unit inthe sugar ester compound (hereinafter this may be referred to as ahydroxyl group content) is at most 3, more preferably at most 1, evenmore preferably zero (0). Controlling the hydroxyl group content to fallwithin the range is preferred since the sugar ester compound may beprevented from moving into the adjacent polarizing element layer tobreak the PVA-iodine complex therein while aged under high temperatureand high humidity condition, and therefore the polarizing elementperformance may be prevented from worsening in aging under hightemperature and high humidity condition.

Preferably, in the sugar ester compound for use in the film of theinvention, an unsubstituted hydroxyl group does not exist and thesubstituents therein are an acetyl group and/or a benzyl group alone.

Regarding the proportion of the acetyl group and the benzyl group in thesugar ester compound, preferably, the proportion of the benzyl group issmaller in some degree. This is because the wavelength dispersioncharacteristics of retardation of the cellulose acylate film of thetype, ΔRe and ΔRe/Re(500) may increase and, when the film isincorporated in a liquid crystal display device, the color shift at thetime of black state could be small. Concretely, the ratio of the benzylgroup to the sum total of all the unsubstituted hydroxyl groups and allthe substituents in the sugar ester compound is preferably at most 60%,more preferably at most 40%.

The sugar ester compounds are available as commercial products such asTokyo Chemical's Aldrich, etc., or may be produced according to knownmethods of converting commercially-available hydrocarbons into esterderivatives thereof (for example, according to the method described inJP-A 8-245678).

Preferably, the sugar ester compound has a number-average molecularweight of from 200 to 3500, more preferably from 200 to 3000, even morepreferably from 250 to 2000.

Specific examples of the sugar ester compounds preferred for use in theinvention are mentioned below; however, the invention is not limited tothe following embodiments.

In the structural formulae mentioned below, R each independentlyrepresents an arbitrary substituent, and plural R's may be the same ordifferent.

TABLE 1 Substituent 1 Substituent 2 degree of degree of MolecularCompound type substitution type substitution Weight 100 acetyl 8 benzyl0 679 101 acetyl 7 benzyl 1 727 102 acetyl 6 benzyl 2 775 103 acetyl 5benzyl 3 817 104 acetyl 0 benzyl 8 1063 105 acetyl 7 benzoyl 1 741 106acetyl 6 benzoyl 2 802 107 benzyl 2 no 0 523 108 benzyl 3 no 0 613 109benzyl 4 no 0 702 110 acetyl 7 phenylacetyl 1 771 111 acetyl 6phenylacetyl 2 847

TABLE 2 Substituent 1 Substituent 2 degree of degree of Com- substi-substi- Molecular pound type tution type tution Weight 201 acetyl 4benzoyl 1 468 202 acetyl 3 benzoyl 2 514 203 acetyl 2 benzoyl 3 577 204acetyl 4 benzyl 1 454 205 acetyl 3 benzyl 2 489 206 acetyl 2 benzyl 3535 207 acetyl 4 phenylacetyl 1 466 208 acetyl 3 phenylacetyl 2 543 209acetyl 2 phenylacetyl 3 619 210 phenylacetyl 1 no 0 298 211 phenylacetyl2 no 0 416 212 phenylacetyl 3 no 0 535 213 phenylacetyl 4 no 0 654

TABLE 3 Substituent 1 Substituent 2 degree of degree of Com- substi-substi- Molecular pound type tution type tution Weight 301 acetyl 6benzoyl 2 803 302 acetyl 6 benzyl 2 775 303 acetyl 6 phenylacetyl 2 831304 benzoyl 2 no 0 551 305 benzyl 2 no 0 522 306 phenylacetyl 2 no 0 579

TABLE 4 Substituent 1 Substituent 2 degree of degree of Com- substi-substi- Molecular pound type tution type tution Weight 401 acetyl 6benzoyl 2 803 402 acetyl 6 benzyl 2 775 403 acetyl 6 phenylacetyl 2 831404 benzoyl 2 no 0 551 405 benzyl 2 no 0 523 406 phenyl ester 2 no 0 579

Preferably, the film of the invention contains the sugar ester compoundin an amount of from 2 to 30% by mass relative to the cellulose acylatetherein, more preferably from 5 to 20% by mass, even more preferablyfrom 5 to 15% by mass.

In case where the film contains the after-mentioned additive having anegative intrinsic birefringence along with the sugar ester compound,the amount of the sugar ester compound (part by mass) relative to theamount of the additive having a negative intrinsic birefringence (partby mass) is preferably from 2 to 10 times (ratio by mass), morepreferably from 3 to 8 times (ratio by mass).

In case where the film contains the after-mentioned polyester-typeplasticizer along with the sugar ester compound, the amount of the sugarester compound (part by mass) relative to the amount of thepolyester-type plasticizer (part by mass) is preferably from 2 to 10times (ratio by mass), more preferably from 3 to 8 times (ratio bymass).

One or more different types of sugar ester compounds mentioned above maybe used in the film of the invention either singly or as combinedtherein.

(Other Additive than Sugar Ester Compound)

The film of the invention may contain any other additive capable ofbeing added to ordinary cellulose acylate films, than theabove-mentioned sugar ester compound.

The additive includes, for example, an additive having a negativeintrinsic birefringence, other plasticizer than the above-mentionedsugar ester compound, fine particles, retardation enhancer, antioxidant,thermal degradation inhibitor, colorant, UV absorbent, etc.

As those additives, preferably used herein are the compounds describedin WO2008-126535.

(1) Additive Having Negative Intrinsic Birefringence:

The film of the invention may contain an additive having a negativeintrinsic birefringence. Compounds having a negative intrinsicbirefringence usable herein as the additive having a negative intrinsicbirefringence are described below.

The compound having a negative intrinsic birefringence means a materialthat exhibits a negative intrinsic birefringence in a cellulose acylatefilm in a specific direction of the film. In this description, theproperty of negative intrinsic birefringence means that the compound hasdouble refractive indices. Whether or not the compound has a negativeintrinsic birefringence could be known, for example, by measuring thebirefringence of a film to which the compound is added and that ofanother film to which the compound is not added, using a birefringencemeter, followed by comparing the data with each other.

The compound having a negative intrinsic birefringence for use in theinvention is not specifically defined. Any known compound having anegative intrinsic birefringence can be used here. For example,preferred are the compounds disclosed in JP-A 2010-46834, [0036] to[0092].

The compound having a negative intrinsic birefringence includes apolymer having a negative intrinsic birefringence and needle-like fineparticles having a negative intrinsic birefringence (includingneedle-like fine particles of a polymer having a negative intrinsicbirefringence). The polymer having a negative intrinsic birefringenceusable in the invention is described below.

The polymer having a negative intrinsic birefringence is a polymer ofsuch that, when a layer thereof with monoaxially-ordered molecularalignment receives light running thereinto, the refractive index of thelight in the alignment direction is smaller than the refractive index ofthe light in the direction perpendicular to the alignment direction.

The polymer having such a negative intrinsic birefringence may be anegative polymer, for example, including a polymer having a specificcyclic structure (discotic ring such as aliphatic-aromatic ring orheteroaromatic ring) in the side chain (for example, styrenic polymersuch as polystyrene, poly(4-hydroxy)styrene, styrene-maleic anhydridecopolymer, as well as polyvinylpyridine), a (meth)acrylic polymer suchas polymethyl methacrylate, a cellulose ester polymer (excluding thosehaving a positive birefringence), a polyester polymer (excluding, thosehaving a positive birefringence), an acrylonitrile polymer, analkoxysilyl polymer, and their polynary (binary, ternary or the like)copolymers. One or more such polymers may be employable here eithersingly or as combined. The copolymers may be block copolymers or randomcopolymers.

Of those, preferred are a polymer having a specific cyclic structure, a(meth) acrylic polymer and an alkoxysilyl polymer; and more preferredare polystyrene, polyhydroxystyrene, polyvinylpyridine and (meth)acrylicpolymer.

Adding a polymer having a specific cyclic structure to the celluloseacylate film is preferred as increasing the Rth of the film.

As the polymer having a specific cyclic structure, preferred for useherein are the polymers having an aliphatic-aromatic ring in the sidechain described in JP-A 2010-46834. Of those, more preferred arepolystyrene and poly(4-hydroxy)styrene; and even more preferred is acopolymer of polystyrene and poly(4-hydroxy)styrene. Thecopolymerization ratio (by mol) of the copolymer of polystyrene andpoly(4-hydroxy)styrene is preferably from 10/90 to 100/0, morepreferably from 20/80 to 90/10.

As the polymer having a specific cyclic structure, also preferred foruse herein is a polymer having a heteroaromatic ring in the side chainsuch as polyvinylpyridine, etc.

When a (meth)acrylic polymer is added to the cellulose acylate film, thefilm may have extremely excellent transparency and its moisturepermeability is extremely small, and the film exhibits excellentproperties as a protective film for polarizer. As the (meth)acrylicpolymer, preferred for use herein are the compounds described in JP-A2009-1696 and WO2008-126535. The (meth)acrylic polymer may have analiphatic-aromatic ring or a heteroaromatic ring in the side chain.

In case where the compound having a negative intrinsic birefringence isa polymer having a negative intrinsic birefringence, its weight-averagemolecular weight is preferably from 500 to 100,000, more preferably from700 to 50,000, even more preferably from 700 to 10,000.

The polymer having a molecular weight of at least 500 and the polymerhaving a molecular weight of at most 100,000 are both good, since theformer is well volatile and the latter is well compatible with celluloseacylate resin and the polymers secure good formation of celluloseacylate films.

Preferably, the compound having a negative intrinsic birefringence isadded to the film of the invention in an amount of from 0 to 20% by massof the cellulose acylate, more preferably from 0 to 15% by mass, evenmore preferably from 0 to 10% by mass.

On the other hand, inc case where the film of the invention is producedaccording to the production method of the invention mentioned below andeven when the film does not contain such a relatively expensive compoundhaving a negative intrinsic birefringence, the film may have goodreversed wavelength dispersion characteristics of retardation.Accordingly, the amount of the compound having a negative intrinsicbirefringence to be added to the film of the invention is preferablysmaller from the viewpoint of reducing the production cost.

(2) Other Plasticizer than Sugar Ester Compound:

Any other plasticizer than the sugar ester compound may be added to thefilm of the invention.

As the other plasticizer, for example, preferred are a phosphate-typeplasticizer, a phthalate-type plasticizer, a trimellitate-typeplasticizer, a pyromellitate-type plasticizer, a polyalcohol-typeplasticizer, a glycolate-type plasticizer, a citrate-type plasticizer, apolyester-type plasticizer (such as fatty acid-terminated polyester-typeplasticizer, aromatic ring-containing polyester-type plasticizer), acarboxylate-type plasticizer, an acrylic polymer, etc.

The other plasticizer for use in the invention is preferably apolyester-type plasticizer having a number-average molecular weight offrom 300 to less than 2000 in order that it does not cause haze of thefilm and it does not bleed out or evaporate from the film.

Not specifically defined, the polyester-type plasticizer preferably hasan aromatic ring or a cycloalkyl ring in the molecule.

For example, an aromatic-terminated polyester-type plasticizerrepresented by the following formula (2) is preferred.

B¹-(G¹-A¹)n-G¹-B¹  (2)

wherein B¹ represents a benzenemonocarboxylic acid residue, G¹represents an alkylene glycol residue having from 2 to 12 carbon atoms,or an arylglycol residue having from 6 to 12 carbon atoms, or anoxyalkylene glycol residue having from 4 to 12 carbon atoms, A¹represents an alkylenedicarboxylic acid residue having from 4 to 12carbon atoms, or an aryldicarboxylic acid residue having from 6 to 12carbon atoms, and n indicates an integer of 1 or more.

The compound represented by the formula (2) is composed of abenzenemonocarboxylic acid residue represented by B¹, an alkylene glycolresidue or an oxyalkylene glycol residue or an arylglycol residuerepresented by G¹, and an alkylenedicarboxylic acid residue or anaryldicarboxylic acid residue represented by A¹.

The benzenemonocarboxylic acid component of the polyester-typeplasticizer for use in the invention includes, for example, benzoicacid, para-tertiary butyl-benzoic acid, ortho-toluic acid, meta-toluicacid, para-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, normalpropylbenzoic acid, aminobenzoic acid, acetoxybenzoic acid, etc. One ormore of these may be used either singly or as combined.

The alkylene glycol component having from 2 to 12 carbon atoms of thepolyester-type plasticizer preferred for use in the invention includesethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol,1,2-butanediol, 1,3-butanediol, 1,2-propanediol,2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,2,2-dimethyl-1,3-propanediol (neopentyl glycol),2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane),2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane),3-methyl-1,5-pentanediol, 1,6-hexanediol,2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol,2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol,1,12-octadecanediol, etc. One or more these glycols may be used hereeither singly or as combined.

The alkylene glycol having from 2 to 12 carbon atoms is especiallypreferred as having excellent compatibility with cellulose acylate.

The oxyalkylene glycol component having from 4 to 12 carbon atoms of thepolyester-type plasticizer preferred for use in the invention includes,for example, diethylene glycol, triethylene glycol, tetraethyleneglycol, dipropylene glycol, tripropylene glycol, etc. One or more theseglycols may be used here either singly or as combined.

The alkylenedicarboxylic acid component having from 4 to 12 carbon atomsof the polyester-type plasticizer preferred for use in the inventionincludes, for example, succinic acid, maleic acid, fumaric acid,glutaric acid, adipic acid, azelaic acid, sebacic acid,dodecanedicarboxylic acid, etc. One or more of these may be used eithersingly or as combined.

The arylenedicarboxylic acid component having from 6 to 12 carbon atomsincludes phthalic acid, terephthalic acid, isophthalic acid,1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, etc.

The number-average molecular weight of the polyester-type plasticizerfor use in the invention preferably falls within a range of from 300 to1500, more preferably from 400 to 1000.

Preferably, the acid value of the plasticizer is at most 0.5 mg KOH/gand the hydroxyl value thereof is at most 25 mg KOH/g, and morepreferably the acid value is at most 0.3 mg KOH/g and the hydroxyl valueis at most 15 mg KOH/g.

As the polyester-type plasticizer for use in the invention, alsopreferred are the polymers described in JP-A 2010-46834, [0141] to[0156].

The polyester-type plasticizer may be produced through ordinarypolycondensation. For example, the polyester may be produced with easeaccording to any of (i) a thermal melt condensation method of directreaction of a dibasic acid and a glycol, or polyesterification orinteresterification of the above-mentioned dibasic acid or its alkylester, for example, a methyl ester of the dibasic acid and a glycol, or(ii) a method of dehydrohalogenation of a chloride of the acid and aglycol. Preferably, the polyester-type plasticizer for use in theinvention is produced through direct reaction.

A polyester-type plasticizer having a high distribution profile in thelow-molecular weight side is extremely highly compatible with celluloseacylate, and can therefore provide a cellulose acylate film having asmall moisture permeability and excellent in transparency.

For controlling the molecular weight of the polymer, any known method isemployable with no limitation. For example, though depending on thepolymerization condition, the molecular weight of the polymer can becontrolled by adding a monovalent acid or a monoalcohol in a method ofterminating the polymer with the monovalent compound.

In this case, a monovalent acid is preferred from the viewpoint of thestability of the polymer. For example, acetic acid, propionic acid,butyric acid or the like is usable. Of those, preferably selected foruse in the invention is one which does not go out of the system duringpolycondensation reaction but which, after the reaction, can be readilyremoved from the system. A mixture of these acids may also be used.

In the direct reaction, the timing of stopping the reaction may becomputed from the amount of water to be formed during the reactionwhereby the number-average molecular weight of the polymer to beproduced can be controlled. In addition, by specifically defining themolar number of the glycol or the dibasic acid to be fed into a reactor,or by controlling the reaction temperature, the molecular weight of thepolymer can be controlled.

The molecular weight of the polyester-type plasticizer for use in theinvention can be determined according to GPC as mentioned above oraccording to a method of terminal quantification (hydroxyl value).

Preferably, the film of the invention contains the other plasticizerthan the sugar ester compound such as the polyester-type plasticizer inan amount of from 1 to 40% by mass of the cellulose acylate therein,more preferably from 5 to 15% by mass.

(Nitrogen-Containing Aromatic Compound-Type Plasticizer)

The film of the invention may contain a nitrogen-containing aromaticcompound-type plasticizer having, as the mother nucleus thereof, any ofpyridine, pyrimidine, triazine or purine and having, as a substituent tobe at any substitutable position of the mother nucleus, any of an alkylgroup, an alkenyl group, an alkynyl group, an amino group, an amidegroup (this means a structure of an acyl group bonding to the compoundvia an amide bond), an aryl group, an alkoxy group, a thioalkoxy group,an alkyl or arylthio group (an alkyl group or an aryl group bonding tothe compound via a sulfur atom), or a heterocyclic group. Thesubstituent of the mother nucleus of the nitrogen-containing aromaticcompound-type plasticizer may be further substituted with any othersubstituent, and the other substituent is not specifically defined. Forexample, in case where the mother nucleus is substituted with an aminogroup, the amino group may be substituted with one or more alkyl groups(in which the alkyl groups may bond to each other to form a ring), orwith —SO₂R′ (R′ means a substituent).

Specific examples of the nitrogen-containing aromatic compound-typeplasticizer are mentioned below, to which, however, the invention shouldnot be restricted.

wherein R¹ to R³ are R¹ to R³, respectively, in the following compoundsC-101 to C-180.

Compound R¹ R² R³ C-101 C-102 C-103 C-104

H o-Me m-Me p-Me H o-Me m-Me p-Me C-105 o-OMe o-OMe C-106 m-OMe m-OMeC-107 p-OMe p-OMe C-108 p-t-Bu p-t-Bu C-109 m-Cl m-Cl C-110 m-F m-FC-111 C-112 C-113

H o-Me m-Me H o-Me m-Me C-114 p-Me p-Me C-115 p-OMe p-OMe C-116 m-OMem-OMe C-117 p-OMe p-OMe C-118 p-t-Bu p-t-Bu C-119 m-Cl m-Cl C-120 m-Fm-F C-121 C-122

H o-Me H o-Me C-123 m-Me m-Me C-124 p-Me p-Me C-125 o-OMe o-OMe C-126m-OMe m-OMe C-127 p-OMe p-OMe C-128 p-t-Bu p-t-Bu C-129 m-Cl m-Cl C-130m-F m-F C-131 C-132

H o-Me H o-Me C-133 m-Me m-Me C-134 p-Me p-Me C-135 o-OMe o-OMe C-136m-OMe m-OMe C-137 p-OMe p-OMe C-138 p-t-Bu p-t-Bu C-139 m-Cl m-Cl C-140m-F m-F C-141 H₂N—* H H C-142 o-Me o-Me C-143 m-Me m-Me C-144 p-Me p-MeC-145 o-OMe o-OMe C-146 m-OMe m-OMe C-147 p-OMe p-OMe C-148 p-t-Bup-t-Bu C-149 m-Cl m-Cl C-150 m-F m-F C-151 C-152 C-153

H o-Me m-Me H o-Me m-Me C-154 p-Me p-Me C-155 o-OMe o-OMe C-156 m-OMem-OMe C-157 p-OMe p-OMe C-158 p-t-Bu p-t-Bu C-159 m-Cl m-Cl C-160 m-Fm-F C-161 C-162 C-163

H o-Me m-Me H o-Me m-Me C-164 p-Me p-Me C-165 o-OMe o-OMe C-166 m-OMem-OMe C-167 p-OMe p-OMe C-168 p-t-Bu p-t-Bu C-169 m-Cl m-Cl C-170 m-Fm-F C-171 C-172 C-173

H o-Me m-Me H o-Me m-Me C-174 p-Me p-Me C-175 o-OMe o-OMe C-176 m-OMem-OMe C-177 p-OMe p-OMe C-178 p-t-Bu p-t-Bu C-179 m-Cl m-Cl C-180 m-Fm-F

wherein R² and R³ are R² and R³, respectively, in the followingcompounds C-181 to C-190.

Compound R² R³ C-181 H H C-182 o-Me o-Me C-183 m-Me m-Me C-184 p-Me p-MeC-185 o-OMe o-OMe C-186 m-OMe m-OMe C-187 p-OMe p-OMe C-188 p-t-Bup-t-Bu C-189 m-Cl m-Cl C-190 m-F m-F

wherein R³ is R³ in the following compounds D-101 to D-110.

Compound R³ D-101 H D-102 o-Me D-103 m-Me D-104 p-Me D-105 o-OMe D-106m-OMe D-107 p-OMe D-108 p-t-Bu D-109 m-Cl D-110 m-F

(3) Fine Particles:

An inorganic compound or a polymer is usable as the fine particles foruse in the invention. Examples of the inorganic compound include silicondioxide, titanium dioxide, aluminium oxide, zirconium oxide, calciumcarbonate, talc, clay, calcined kaolin, calcined calcium silicate,calcium silicate hydrate, aluminium silicate, magnesium silicate andcalcium phosphate.

As the fine particles, preferred are those containing silicon asreducing the haze of the film, and more preferred is silicon dioxide.

Preferably, the fine particles have a primary particle size of from 5 to50 nm, more preferably from 7 to 20 nm.

Preferably, the fine particles are in the film mainly as secondaryaggregates thereof having a particle size of from 0.05 to 0.3 μm.

As the fine particles of silicon dioxide, for example, usable arecommercial products of Aerosil R972, R972V, R974, R812, 200, 200V, 300,R202, OX50 and TT600, NAX50 (all by Nippon Aerosil).

Fine particles of zirconium oxide are sold on the market as trade namesof Aerosil R976 and R811 (by Nippon Aerosil), and these can be usedhere.

Examples of the polymer include silicone resin, fluororesin and acrylicresin. Silicone resin is preferred, and more preferred is one having athree-dimensional network structure. For example, Tospearl 103, 105,108, 120, 145, 3120 and 240 are sold as commercial products (all byToshiba Silicone), and these are usable herein.

Of those, Aerosil 200V and Aerosil 972V are especially preferred as moreeffectively lowering the friction coefficient of the cellulosederivative film with keeping the haze of the film low.

The content of the fine particles relative to the cellulose acylate inthe cellulose film of the invention is preferably from 0.05 to 1% bymass, more preferably from 0.1 to 0.5% by mass. In case where the filmis a multilayered cellulose derivative film produced according to aco-casting method, the film contains the fine particles in that contentpreferably in the surface thereof.

(4) Retardation Enhancer:

The film of the invention may contain a retardation enhancer. Containinga retardation enhancer, the film can exhibit high retardation eventhough stretched at a low draw ratio. On the other hand, when the filmof the invention is produced according to the production method of theinvention to be mentioned below, the film can secure good retardationeven though not containing a retardation enhancer.

The type of the retardation enhancer is not specifically defined. Theretardation enhancer includes rod-shaped compounds or compounds having acyclic structure such as a cycloalkane or aromatic ring, and theabove-mentioned non-phosphate compounds having the ability to enhanceretardation. As the cyclic structure-having compounds, preferred arediscotic compounds. As the rod-shaped or discotic compounds, compoundshaving at least two aromatic rings are preferred as the retardationenhancer for use herein.

Two or more different types of retardation enhancers may be used here ascombined.

Preferably, the retardation enhancer has a maximum absorption in awavelength region of from 250 to 400 nm, more preferably substantiallynot having an absorption in a visible region.

As the retardation enhancer, for example, usable are the compoundsdescribed in JP-A 2004-50516 and 2007-86748 and the compounds describedin JP-A 2010-46834, to which, however, the invention is not limited.

As the discotic compound for use herein, for example, preferred are thecompounds described in EP 0911656-A2, the triazine compounds describedin JP-A 2003-344655, and the triphenylene compounds described in JP-A2008-150592, [0097] to [0108].

The discotic compounds usable herein may be produced according to knownmethods, for example, according to the method described in JP-A2003-344655, the method described in JP-A 2005-134884, etc.

In addition to the above-mentioned discotic compounds, also preferredfor use herein are rod-shaped compounds having a linear molecularstructure; and for example, the rod-shaped compounds described in JP-A2008-150592, [0110] to [0127] are preferred.

(5) Antioxidant, Thermal Degradation Inhibitor:

As an antioxidant and a thermal degradation inhibitor, any known onesare usable in the invention. In particular, preferred are lactonecompounds, sulfur compounds, phenolic compounds, double bond-havingcompounds, hindered amines, phosphorus compounds. As the antioxidant andthe thermal degradation inhibitor for use herein, preferred are thecompounds described in WO2008-126535.

(6) Colorant:

The film of the invention may contain a colorant. Colorant generallyincludes dye and pigment; but in the invention, the colorant is meant toindicate a substance having an effect of making the liquid crystal panelhave a bluish tone, or an effect of controlling the yellow index of thepanel or reducing the haze thereof. As the colorant, preferred for useherein are the compounds described in WO2008-126535.

<Properties of Cellulose Acylate Film> (Internal Haze)

The cellulose acylate film of the invention has an internal haze of atmost 0.1%.

The haze means the haze value (%) measured according to JIS K7136.

The internal haze of the film of the invention is determined as follows:A few drops of glycerin are applied onto both surfaces of the celluloseacylate film to be analyzed, the film is sandwiched between two glassplates (MICRO SLIDE GLASS Lot No. S9213, by Matsunami) each having athickness of 1.3 mm, and the haze value (%) of the sample is measured.On the other hand, a few drops of glycerin are put between two glassplates, and the haze value (%) thereof is measured. The latter value issubtracted from the former value to give the internal haze value (%) ofthe film sample.

The haze of the cellulose acylate film is measured with a haze meter(NDH2000, by Nippon Denshoku Kogyo). Briefly, a film sample to beanalyzed is left in an environment at 23° C. and a relative humidity of55% for 24 hours, and its haze is measured in the same environment.

Preferably, the internal haze of the cellulose acylate film of theinvention is at most 0.05%, more preferably at most 0.04%.

In general, it is said that the haze of film is preferably smaller.However, merely low total haze of film is insufficient for increasingthe front contrast of a display device, and the present inventors havecontrolled the internal haze of the film to fall within the above rangeand have succeeded in increasing the front contrast of a liquid crystaldisplay device.

(Re, Rth)

Of the film of the invention, the in-plane retardation and thethickness-direction retardation at a wavelength of 550 nm satisfy thefollowing formulae (1) and (2):

40 nm≦Re(550)≦60 nm  (1)

wherein Re(550) means the in-plane retardation of the film at awavelength of 550 nm,

100 nm≦Rth(550)≦140 nm  (2)

wherein Rth(550) means the thickness-direction retardation of the filmat a wavelength of 550 nm.

Preferably, the film of the invention expresses the retardation, withinthe above range, from the viewpoint of improving the contrast of aliquid crystal display device and of reducing the color shift thereof atthe time of black state.

Preferably, Re(550) is from 45 to 60 nm, more preferably from 48 to 60nm.

Preferably, Rth(550) is from 105 to 135 nm, more preferably from 105 to130 nm.

(Rth(550)/d)

Preferably, the film of the invention satisfies the following formula(6), from the viewpoint of satisfying both thickness reduction andsufficient Rth expression of the film and of reducing the material costof the film.

1.5×10⁻³ <Rth(550)/d  (6)

wherein Rth(550) means the thickness-direction retardation (unit: nm) ofthe film at a wavelength of 550 nm, and d means the thickness (unit: mm)of the film.

More preferably, Rth(550)/d is from 1.5 to 3.0×10⁻³, even morepreferably from 1.6 to 2.5×10⁻³.

(Wavelength Dispersion Characteristics of Retardation)

Preferably, the film of the invention has reversed wavelength dispersioncharacteristics of retardation of such that the difference between thein-plane retardation thereof at a wavelength of 630 nm, Re(630), and thein-plane retardation thereof at a wavelength of 450 nm, Re(450), or thatis, ΔRe (ΔRe=Re(630)−Re(450)) is positive, from the viewpoint that, whenthe film is incorporated in a liquid crystal display device, it could bemore effective for reducing the color shift in the device at the time ofblack state.

Preferably, ΔRe/Re(550) of the film of the invention satisfies thefollowing formula (4) from the same viewpoint as above.

0.02≦ΔRe/Re(550)≦0.28  (4)

ΔRe=Re(630)−Re(450)  (4′)

wherein Re(630) means the in-plane retardation of the film at awavelength of 630 nm; Re(450) means the in-plane retardation of the filmat a wavelength of 450 nm; Re(550) means the in-plane retardation of thefilm at a wavelength of 550 nm.

Also preferably, ΔRe/Re(550) of the film of the invention satisfies thefollowing formula (5) from the viewpoint that, when the film isincorporated in a liquid crystal display device, it could be moreeffective for more remarkably reducing the color shift in the device atthe time of black state.

0.11≦ΔRe/Re(550)≦0.23  (5)

ΔRe=Re(630)−Re(450)  (5′)

Preferably, the film of the invention is a biaxial optical compensatoryfilm.

The biaxial optical compensatory film means that nx, ny and nz of theoptical compensatory film all differ from each other, in which nx meansthe refractive index in the in-plane slow axis direction, ny means thein-plane refractive index in the direction perpendicular to nx, and nzmeans the refractive index in the direction perpendicular to nx and ny.More preferably in the invention, nx>ny>nz.

The film of the invention having the biaxial optical property ispreferred in that, when it is incorporated in a liquid crystal displaydevice, especially in a VA-mode liquid crystal display device and whenthe device is watched in an oblique direction, the problem of colorshift can be reduced.

In this description, Re(λ) and Rth(λ) each mean the in-plane retardationand the thickness-direction retardation, respectively, of a film at awavelength of λ. Unless otherwise specifically indicated in thisdescription, the wavelength λ is 550 nm. Re(λ) is measured by applying alight having a wavelength of λ nm to a film sample in the normaldirection of the film, using KOBRA 21ADH (by Oji ScientificInstruments). Rth(λ) is determined as follows: With the in-plane slowaxis (determined by KOBRA 21ADH) taken as the tilt axis (rotation axis)of the film (in case where the film has no slow axis, the rotation axisof the film may be in any in-plane direction of the film), Re(λ) of thefilm is measured at 6 points in all thereof, from the normal directionof the film up to 50 degrees on one side relative to the normaldirection thereof at intervals of 10°, by applying a light having awavelength of λ nm from the tilted direction of the film. Based on thethus-determined retardation data of Re(λ), the assumptive meanrefractive index and the inputted film thickness, Rth(λ) of the film iscomputed with KOBRA 21ADH. Apart from this, Re(λ) may also be measuredas follows: With the slow axis taken as the tilt axis (rotation axis) ofthe film (in case where the film has no slow axis, the rotation axis ofthe film may be in any in-plane direction of the film), the retardationis measured in any desired two directions, and based on thethus-determined retardation data, the assumptive mean refractive indexand the inputted film thickness, Rth is computed according to thefollowing formulae (A) and (B). In this, for the assumptive meanrefractive index, referred to are the data in Polymer Handbook (JohnWiley & Sons, Inc.) or the data in the catalogues of various opticalfilms. Films of which the mean refractive index is unknown may beanalyzed with an Abbe's refractiometer to measure the mean refractiveindex thereof. Data of the mean refractive index of some typical opticalfilms are mentioned below. Cellulose acylate (1.48), cycloolefin polymer(1.52), polycarbonate (1.59), polymethyl methacrylate (1.49),polystyrene (1.59). With the assumptive mean refractive index and thefilm thickness inputted thereinto, Kobra 21ADH can compute nx, ny andnz. From the thus-computed data nx, ny and nz, Nz=(nx−nz)/(nx−ny) isinduced.

$\begin{matrix}{{{Re}(\theta)} = {\left\lbrack {{nx} - \frac{{ny} \times {nz}}{\sqrt{\begin{matrix}{\left\{ {{ny}\; {\sin \left( {\sin^{- 1}\left( \frac{\sin \left( {- \theta} \right)}{nx} \right)} \right)}} \right\}^{2} +} \\\left\{ {{nz}\; {\cos \left( {\sin^{- 1}\left( \frac{\sin \left( {- \theta} \right)}{nx} \right)} \right)}} \right\}^{2}\end{matrix}}}} \right\rbrack \times \frac{d}{\cos \left\{ {\sin^{- 1}\left( \frac{\sin \left( {- \theta} \right)}{nx} \right)} \right\}}}} & (A)\end{matrix}$

In this, Re(θ) means the retardation of the film in the direction tiltedby an angle θ from the normal direction to the film; nx, ny and nz eachmean the refractive index in each main axis direction of an indexellipsoid; and d means the thickness of the film.

Rth=((nx+ny)/2−nz)×d  (B)

In this, the mean refractive index n is needed as the parameter, forwhich used are the data measured with an Abbe's refractiometer (Atago's“Abbe Refractiometer 2-T”).

(Dimensional Change)

Of the film of the invention, the dimensional change before and after 24hours at 60° C. and at a relative humidity of 90% satisfies thefollowing formula (3) in the film conveying direction and in thedirection perpendicular thereto:

−0.5%≦{(L′−L0)/L0}×100≦0.5%  (3)

wherein L0 means the length (unit: mm) of the film before aged for 24hours at 60° C. and at a relative humidity of 90%; and L′ means thelength (unit: mm) of the film after aged for 24 hours at 60° C. and at arelative humidity of 90% and further after conditioned for 2 hours.

Preferably, the dimensional change of the film of the invention beforeand after 24 hours at 60° C. and at a relative humidity of 90% is atmost 0.3% in the film conveying direction, more preferably at most 0.2%,even more preferably at most 0.1%.

Preferably, the dimensional change of the film of the invention beforeand after 24 hours at 60° C. and at a relative humidity of 90% is atmost 0.4% in the direction perpendicular to the film conveyingdirection, more preferably at most 0.3%, even more preferably at most0.2%.

(Glass Transition Temperature of Cellulose Acylate Film)

Not contradictory to the scope and the spirit of the invention, theglass transition temperature of the cellulose acylate film of theinvention is not specifically defined.

The glass transition temperature of the unstretched cellulose acylatefilm of the invention may differ from the glass transition temperatureof the stretched film. Unless otherwise specifically indicated, Tgreferred to in the production method for the cellulose acylate film ofthe invention to be mentioned below means the glass transitiontemperature of the unstretched cellulose acylate film.

(Layer Constitution of Cellulose Acylate Film)

The film of the invention may be a single-layer film or may have alaminate structure of two or more layers, but is preferably asingle-layer film.

(Film Thickness)

Preferably, the film of the invention has a thickness of from 20 to 90μm from the viewpoint of reducing the production cost, more preferablyfrom 30 to 90 μm, even more preferably from 40 to 80 μm, still morepreferably from 40 to 70 μm. In case where the film of the invention isa laminate film, the overall film thickness preferably falls within theabove range.

(Film Width)

Preferably, the film width of the invention is at least 1000 mm, morepreferably at least 1500 mm, even more preferably at least 1800 mm.

[Production Method for Cellulose Acylate Film of the Invention]

The production method for the cellulose acylate film of the invention(hereinafter referred to as the production method of the invention)comprises a step of forming a polymer solution that comprises acellulose acylate and a sugar ester compound containing from 1 to 12pyranose structures or furanose structures where at least one hydroxylgroup is esterified, into a film, a step of stretching the film, and astep of processing the stretched film for high temperature and highhumidity treatment under the condition satisfying the following formulae(7) and (8):

70° C.≦temperature of the treatment≦140° C.  (7)

250 g/m³≦volumetric humidity of the treatment≦400 g/m³  (8)

The production method of the invention is described below.

The production method comprises formation of the above-mentionedcellulose acylate-containing film according to a solution casting methodor a melt casting method. From the viewpoint of bettering the filmsurface condition, the production method preferably comprises a step offorming the cellulose acylate-containing film in a mode of solutioncasting film formation.

The production method of the invention is described below with referenceto an embodiment of solution casting film formation; however, theinvention is not limited to the mode of solution casting film formation.In case where the film of the invention is produced according to a meltcasting method, any known method is employable.

<Polymer Solution>

In the solution casting film formation method, a polymer solutioncontaining cellulose acylate and optionally various additives (celluloseacylate solution) is formed into a web. The polymer solution for use inthe solution casting film formation method (hereinafter this may bereferred to as cellulose acylate solution or dope) is described below.

(Solvent)

The cellulose acylate for use in the invention is dissolved in a solventto form a dope, which is cast on a substrate to form a film thereon. Inthis step, the solvent must be evaporated away after extrusion orcasting, and therefore, a volatile solvent is preferably used.

Further, the solvent is one not reacting with a reactive metal compound,a catalyst or the like and not dissolving the casting substrate. Two ormore different types of solvents may be used here as combined.

As the case may be, a cellulose acylate and a hydrolyzable andpolycondensable reactive metal compound may be dissolved indifferentsolvents, and the resulting solutions may be mixed later.

An organic solvent capable of well dissolving the cellulose acylate isreferred to as a good solvent, and an organic solvent exhibiting themain effect for the dissolution and used in a major amount is referredto as a main (organic) solvent.

Examples of the good solvent include ketones such as acetone, methylethyl ketone, cyclopentanone, cyclohexanone, etc.; ethers such astetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolan, 1,2-dimethoxyethane,etc.; esters such as methyl formate, ethyl formate, methyl acetate,ethyl acetate, amyl acetate, γ-butyrolactone, etc.; as well as methylcellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide,acetonitrile, dimethyl sulfoxide, sulforane, nitroethane, methylenechloride, methyl acetacetate, etc. Preferred are 1,3-dioxolan, THF,methyl ethyl ketone, acetone, methyl acetate and methylene chloride.

Preferably, the dope contains from 1 to 40% by mass of an alcohol havingfrom 1 to 4 carbon atoms, in addition to the above-mentioned organicsolvent.

The alcohol serves as a gelling solvent in such a manner that, after thedope has been cast on a metal support, the solvent begins to evaporateand the proportion of the alcohol in the dope increases whereby the web(the dope film formed by casting the cellulose acylate dope on a supportmay be referred to as web) may be readily gelled and may be well peeledfrom the metal support. In case where the proportion of the alcohol issmall, it may play a role in promoting the dissolution of celluloseacylate in a chlorine-free organic solvent, or may plays a role inretarding the gellation and precipitation of reactive metal compound andretarding the viscosity increase of the dope.

The alcohol having from 1 to 4 carbon atoms includes methanol, ethanol,n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol,propylene glycol monomethyl ether, etc.

Of those, preferred is ethanol as having the advantages of excellentstability in dope, relatively low boiling point, good dryability andnontoxicity. These organic solvents do not have the ability to dissolvecellulose acylate by themselves and are therefore poor solvents.

The cellulose acylate to constitute the cellulose acylate film of theinvention contains a hydroxyl group or a hydrogen-bonding functionalgroup of esters, ketones or the like, and therefore it is desirable thatthe solvent contains an alcohol in an amount of from 5 to 30% by mass ofthe whole solvent, more preferably from 7 to 25% by mass, even morepreferably from 10 to 20% by mass, from the viewpoint of reducing thefilm peeling load from the casting support.

Controlling the alcohol content could facilitate the of Re and Rth ofthe cellulose acylate film produced according to the production methodof the invention. Concretely, when the alcohol content is increased,then the drying temperature (heat treatment temperature) beforestretching in the production method of the invention to be mentionedbelow could be set relatively low, whereby the ultimate range of Re andRth could be enlarged more.

In the invention, it is also effective to make the film contain a smallamount of water for controlling the dope viscosity, for increasing thewet film strength in drying and for increasing the dope intensity indrum casting. For example, water may be in the dope in an amount of from0.1 to 5% by mass of the whole dope, preferably from 0.1 to 3% by mass,more preferably from 0.2 to 2% by mass.

Examples of the combination of organic solvents preferred for use as thesolvent for the polymer solution in the invention are described in JP-A2009-262551.

If desired, a non-halogen organic solvent may be used as the mainsolvents, and its details are described in (No. 2001-1745, published bythe Hatsumei Kyokai on Mar. 15, 2001).

The cellulose acylate concentration in the polymer solution in theinvention is preferably from 5 to 40% by mass, more preferably from 10to 30% by mass, most preferably from 15 to 30% by mass.

The cellulose acylate concentration can be so controlled that it couldreach a predetermined level in the stage of dissolving cellulose acylatein a solvent. If desired, a solution having a low concentration (forexample, having a concentration of from 4 to 14% by mass) is previouslyprepared, and it may be concentrated by evaporating the solvent. Also ifdesired, a high-concentration solution is previously prepared and it maybe diluted. Adding an additive may lower the cellulose acylateconcentration.

The time for additive addition may be suitably determined depending onthe type of the additive.

The solvent that is most preferred for dissolving the polymer compound,cellulose acylate in a high concentration with satisfying the abovecondition is a mixed solvent of methylene chloride/ethyl alcohol of from95/5 to 80/20. Alternatively, a mixed solvent of methyl acetate/ethylalcohol of from 60/40 to 95/5 may be preferably used.

<Details of Processing Steps> (1) Dissolution Step:

This is a step of dissolving a cellulose acylate in an organic solventcomprising mainly a good solvent for the cellulose acylate in adissolver with stirring therein, to thereby form a dope, or a step ofmixing an additive solution in a cellulose acylate solution to form adope.

For dissolution of cellulose acylate, employable are various dissolutionmethods such as a method to be attained under normal pressure, a methodto be attained at a temperature not higher than the boiling point of themain solvent, a method to be attained under pressure at a temperaturenot lower than the boiling point of the main solvent, a method ofcooling dissolution as in JP-A 9-95544, 9-95557 or 9-95538, a method tobe attained under high pressure as in JP-A 11-21379, etc. Especiallypreferred is the method to be attained under pressure at a temperaturenot lower than the boiling point of the main solvent.

Preferably, the cellulose acylate concentration in the dope is from 10to 35% by mass. An additive is added to the dope during or afterdissolution and is again dissolved and dispersed therein, then theresulting dope is filtered through a filtering material and defoamed,and thereafter fed to the next step with a feeding pump.

(2) Casting Step:

This is a step of feeding the dope to a pressure die via a feeding pump(for example, pressure metering pump), and casting the dope to thecasting position of an endlessly running endless metal belt, forexample, a stainless belt, or of a rotating metal support such as ametal drum or the like, through a pressure die slit.

Preferred is a pressure die of which the slit form of the nozzle can beregulated to facilitate uniform film thickness. The pressure dieincludes a coathanger die, a T-die and the like, any of which isfavorably usable here. The surface of the metal support ismirror-finished. For increasing the film formation speed, two or morepressure dies may be provided for a metal support and the dope may bedivided for multilayer formation. Multiple dopes may be simultaneouslycase according to a co-casting method to produce a laminate-structuredfilm.

(3) Solvent Evaporation Step:

This is a step of heating the web (the precursor that is prior to afinished cellulose acylate film and contains much solvent is referred toas web) on the metal support so as to remove the solvent from the web tosuch a degree that the web can be released from the metal support.

For solvent evaporation, there may be employed a method of applying anair blow to the side of the web and/or a method of heating the back ofthe metal support with a heating liquid, a method of heating both thesurface and the back of the web by radiation heat, etc. Preferred is themethod of heating the back with a heating liquid, as securing gooddrying efficiency. Also preferred is combination of these methods. Inthe method of heating the back with a heating liquid, preferably, theback of the support is heated at a temperature not higher than theboiling point of the main solvent of the organic solvent used in thedope or of the organic solvent having the lowest boiling point.

(4) Peeling Step:

This is a step of peeling the web from which the solvent has beenevaporated away on the metal support, at the peeling position. Thepeeled web is then fed to the next step. When the residual solventamount (represented by the formula mentioned below) in the web to bepeeled is too large, then the web may be difficult to peel, or on thecontrary, when the web is too much dried on the metal support and thenpeeled, then a part of the web may be broken or cut along the way.

In this, as a method of increasing the film formation speed (in whichthe film formation speed may be increased by peeling the web at a timewhen the residual solvent amount is as large as possible), there may bementioned a gel casting method. For example, there are a method ofadding a poor solvent for cellulose acylate to the dope, then castingthe dope and gelling it; and a method of gelling the dope with loweringthe temperature of the metal support. The dope may be gelled on themetal support to thereby increase the strength of the film to be peeled,thereby increasing the film formation speed.

Preferably, the residual solvent amount in the web on the metal supportin peeling the web is controlled to fall within a range of from 5 to150% by mass, depending on the condition of the drying load intensity,the length of the metal support, etc. However, in case where the web ispeeled at a time when the residual solvent amount therein is larger, theresidual solvent amount in peeling will be determined in considerationof both the economical film formation speed and the film quality. In theinvention, the temperature of the peeling position on the metal supportis preferably from −50 to 40° C., more preferably from 10 to 40° C.,most preferably from 15 to 30° C.

Preferably, the residual solvent amount in the web at the peelingposition is from 10 to 150% by mass, more preferably from 10 to 120% bymass.

The residual solvent amount may be expressed by the following formula:

Residual Solvent Amount (% by mass)={(M−N)/N}×100

wherein M is the mass of the web at any point, and N is the mass of theweb having the mass of M after dried at 110° C. for 3 hours.

(5) Drying or Heat Treatment Step, Stretching Step:

In the production method of the invention, preferably, the film isstretched at a temperature not higher than (Tg−5° C.) in the stretchingstep, from the viewpoint of increasing the optical appearance relativeto the thickness of the cellulose acylate film to be obtained, or thatis, increasing Rth(550)/d of the film (in which Tg means the glasstransition temperature (unit: ° C.) of the unstretched cellulose acylatefilm). In particular, more preferably, the cellulose acylate film notheated at all at a temperature not lower than Tg−5° C. is stretched at atemperature not lower than Tg−5° C. in the stretching step.

After the peeling step, preferably, the web is dried in a drying unitwhere the web is led to alternately pass through multiple rolls disposedtherein and/or in a tenter unit where the web is clipped at both sidesthereof and conveyed therethrough.

In the production method of the invention, the web may be heat-treatedor may not be heat-treated before stretched, but in case where the webis heat-treated, it is desirable that the web is not heated at all at atemperature not higher than Tg−5° C. where Tg is the glass transitiontemperature of the cellulose acylate film.

According to the conventional technique in WO2008-126535, the filmcapable of increasing the panel contrast when incorporated in a liquidcrystal display device is produced by heating the unstretched celluloseacylate film at a temperature higher than the stretching temperature ofthe film, and in particular, the unstretched film is preferably heatedat a temperature higher than the stretching temperature by 20° C. ormore. When the film production method includes the heating step that isintrinsically unnecessary for stretching the film for retardationexpression, then the fuel cost noticeably increases and the method mayrequire some additional heating means or apparatus than the stretchingapparatus. Accordingly, the conventional film for increasing the displaypanel contrast is unsatisfactory from the viewpoint of the productioncost, and it is desired to lower the heat treatment temperature tothereby significantly reduce the production cost. However, theinventors' investigations have revealed that, when the heat treatmenttemperature for the film described in Examples in WO2008-126535 islowered, then the display panel front contrast greatly lowers.Accordingly, the production cost for the conventional film capable ofincreasing the display panel contrast could not be lowered any more inview of the production process of the film.

In a preferred embodiment of the invention, even when the film is notheated at all at a temperature not lower than Tg−5° C. before stretched,the total haze and the internal haze of the film could be within thescope of the invention since in the film of the invention, theabove-mentioned sugar ester compound is added to the cellulose acylateand since the film is stretched at the temperature mentioned below.Further, the film of the preferred embodiment of the invention canincrease the panel contrast when incorporated in a liquid crystaldisplay device even though the production cost is lower than before.

In heat treatment, if any, in the invention, the heat treatmenttemperature is preferably not higher than Tg−5° C., more preferably fromTg−20° C. to lower than Tg−5° C., even more preferably from Tg−15° C. tolower than Tg−5° C.

Also preferably, the heat treatment time is at most 30 minutes, morepreferably at most 20 minutes, even more preferably at most 10 minutesor so.

For drying and heat treatment, in general, a hot air blow is applied toboth surfaces of the web; but in place of air, a microwave may beapplied thereto for heating. The temperature, the air blow amount andthe time may vary depending on the solvent to be used; and suitableconditions may be selected in accordance with the type and thecombination of the solvents to be used.

In the production method of the invention, the film may be stretched inany direction of the film conveying direction (hereinafter referred toas machine direction) or in the direction perpendicular to the filmconveying direction (hereinafter referred to as lateral direction), butis preferably stretched in the lateral direction from the viewpoint ofmaking the film express the desired retardation. More preferably, thefilm is stretched biaxially both in the machine direction and in thelateral direction. The stretching may be attained in one stage or inmultiple stages.

Preferably, the draw ratio in stretching the film in the film conveyingdirection is from 0 to 20%, more preferably from 0 to 15%, even morepreferably from 0 to 10%. The draw ratio (elongation) in stretching thecellulose acylate web may be attained by the peripheral speed differencebetween the metal support speed and the peeling speed (peel roll draw).For example, in case where an apparatus having two nip rolls is used,the rotation speed of the nip roll on the outlet side is made fasterthan that of the nip roll on the inlet side, whereby the celluloseacylate film may be stretched preferably in the conveying direction(machine direction). The stretching may control the retardation of thefilm.

“Draw ratio (%)” as referred to herein is computed according to thefollowing formula:

Draw Ratio (%)=100×{(length after stretching)−(length beforestretching)}/(length before stretching).

The draw ratio in stretching the film in the direction perpendicular tothe film conveying direction is preferably from more than 20% to 60%,more preferably from 25 to 55%, even more preferably from 25 to 50%.

In the method of stretching the film in the direction perpendicular tothe film conveying direction in the invention, preferably used is atenter apparatus.

In biaxially stretching the film, for example, the film may be relaxedby from 0.8 to 1.0 time in the machine direction to thereby make thefilm have the desired retardation. The draw ratio in stretching may bedefined depending on the intended optical properties of the film. Inproducing the cellulose acylate film of the invention, the film may bemonoaxially stretched in the machine direction.

In the production method of the invention, the stretching temperature ispreferably not higher than Tg−5° C. The stretching within the range ishereinafter referred to as low-temperature stretching. Low-temperaturestretching of the formed film is favorable as increasing the Rth of thefilm of the invention without increasing the film thickness, or that is,as increasing more Rth(550)/d of the film. Not adhering to any theory,the polymer and the additive in the film would be more hardly orientedduring the low-temperature stretching than during high-temperaturestretching, and therefore the film could express Re not lowering Rththereof through the low-temperature stretching.

On the other hand, in case where an ordinary known cellulose acylatefilm is stretched in a mode of low-temperature stretching, its harmfulresults are that the dimensional change of the film in high temperatureand high humidity environments may increase and the haze of the film mayalso increase. Not adhering to any theory, the harmful results would becaused because residual strain readily remains in film after thelow-temperature stretching and some crazes are readily formed in thefilm during the low-temperature stretching.

As opposed to this, in the production method of the invention, the filmis, after the stretching step, processed in the high temperature andhigh humidity treatment step under the specific condition to bementioned below, in which, therefore, the residual strain generatedthrough the low-temperature stretching can be released; and therefore inthe method including the low-temperature stretching step, the effect ofthe invention can be well secured and the film produced can enjoy theeffect of increasing the Rth through the low-temperature stretchingtreatment.

In a more preferred embodiment of the production method of theinvention, a film of cellulose acetate having a low degree of acetylsubstitution (especially cellulose acetate having a degree of acetylsubstitution of from 2.0 to 2.6) is stretched in a mode oflow-temperature stretching, whereby the film can be prevented fromhaving a haze caused by the low-temperature stretching treatment. Notadhering to any theory, when a cellulose acetate having a low degree ofacetyl substitution is used as the cellulose acylate in the invention,the cellulose acetate having a low degree of acetyl substitution hashigh compatibility with the above-mentioned sugar ester compound, andtherefore it is expected that the two may disperse uniformly with nophase separation of the additives during low-temperature stretching.Accordingly, the stretching stress may be so controlled as to beuniformly given to the whole web, and the stretched film can beprevented from having crazes to be often formed during low-temperaturestretching. As a result, the internal haze of the film producedaccording to the production method of the invention can be controlled tofall within the above-mentioned preferred range.

Preferably, the stretching temperature is from Tg−50° C. to Tg−5° C.,more preferably from Tg−40° C. to Tg−5° C.

Apart from the definition by Tg of the unstretched film, the lowermostlimit of the stretching temperature is preferably higher than 150° C.,more preferably 160° C. or higher. The uppermost limit of the stretchingtemperature is preferably not higher than 170° C.

If desired, the film may be dried after the stretching step and beforethe high temperature and high humidity treatment step to be mentionedbelow. In case where the film is dried after the stretching step andbefore the high temperature and high humidity treatment step to bementioned below, the drying temperature, the drying air blow amount andthe drying time may vary depending on the solvent to be used, and may besuitably selected in accordance with the type and the combination of thesolvents to be used. In the invention, preferably, the dryingtemperature after the stretching step and before the high temperatureand high humidity treatment step to be mentioned below is lower than thestretching temperature in the stretching step, from the viewpoint ofincreasing the panel front contrast when the film is incorporated in aliquid crystal display device.

(6) High Temperature and High Humidity Treatment Step:

The production method of the invention includes a step of processing thestretched film for high temperature and high humidity treatment underthe condition satisfying the following formulae (7) and (8):

70° C.≦temperature of the treatment≦140° C.  (7)

250 g/m³≦volumetric humidity of the treatment≦400 g/m³  (8)

In the above-mentioned preferred embodiment of the production method ofthe invention, the film processed through the low-temperature stretchingtreatment may have desired optical properties in some degree, however,the dimensional stability of the film in aging in high temperature andhigh humidity environments could not be still improved completely. Notadhering to any theory, when a film having a large dimensional change isincorporated in a liquid crystal display device, the problem to occur iscaused by the irreversible change in the film dimension to occur whenthe device is kept in a condition at 60° C. and at a relative humidityof 90% for a long period of time. To solve the problem, the productionmethod of the invention includes high temperature and high humiditytreatment of the stretched film under the condition satisfying theabove-mentioned formulae (7) and (8) to thereby positively generateirreversible change in the film being produced. As a result, when thecellulose acylate film produced according to the production method ofthe invention is mounted on a liquid crystal display device, it mayprevent the generation of corner unevenness (display unevenness to occurin high temperature and high humidity treatment) in oblique directionsto the liquid crystal display panel.

In a more preferred embodiment of the production method of theinvention, a cellulose acetate having a low degree of acetylsubstitution (especially a cellulose acetate having a degree of acetylsubstitution of from 2.0 to 2.6) is used to enhance the opticalappearance of the film and the reversed wavelength dispersioncharacteristic thereof. The cellulose acetate having such a low degreeof acetyl substitution is more advantageous from the viewpoint of theoptical appearance and the reversed wavelength dispersioncharacteristic, than a cellulose acetate propionate having the samedegree of acyl substitution (hereinafter referred to as CAP) or than acellulose acylate having any other acyl substituent than acetyl groupand having the same degree of acyl substitution (for example, celluloseacetate phthalate described in JP-A 2009-1696). However, the celluloseacetate having a low degree of acetyl substitution has a higher watercontent than the cellulose acylate having any other acyl substituentthan acetyl group and having the same degree of acyl substitution.Accordingly, in case where the cellulose acetate having a low degree ofacetyl substitution is formed into a film, it is expected that thedimensional stability of the formed film would be worsened more.However, in the production method of the invention where a celluloseacetate having a low degree of acetyl substitution is used and where thestretched film is processed for high temperature and high humiditytreatment under the specific condition satisfying the above-mentionedformulae (7) and (8), the film of the invention can secure its effectand the dimensional change thereof can be fully reduced. As a result, incase where the cellulose acylate film obtained in the more preferredembodiment of the production method of the invention is mounted on aliquid crystal display device, the display contrast of the liquidcrystal display device can be further enhanced, the color shift indisplay panel can be reduced, and the generation of corner unevenness inoblique directions to the liquid crystal display panel (displayunevenness to occur in high temperature and high humidity treatment) canbe sufficiently prevented.

Preferably, the high temperature and high humidity treatment temperatureis from higher than 70° C. to 125° C., more preferably from 80 to 120°C., even more preferably from 90 to 110° C. The high temperature andhigh humidity treatment temperature as referred to herein means thetemperature of the cellulose acylate film that has been kept in contactwith a contact vapor.

Preferably, the volumetric humidity in high temperature and highhumidity treatment is from 280 to 390 g/m³, more preferably from 290 to350 g/m³, even more preferably from 290 to 330 g/m³.

In a more preferred embodiment thereof, the production method of theinvention is based on the finding that the high temperature and highhumidity treatment of the cellulose acylate film having a low degree ofsubstitution (concretely, cellulose acylate film having a degree of acylsubstitution of from 2.0 to 2.6, especially cellulose acetate filmhaving a degree of acetyl substitution of from 2.0 to 2.6) must beattained under a strictly controlled volumetric humidity condition. Forexample, when a volumetric humidity condition most suitable for acellulose acylate film having a degree of acyl substitution of about 2.9or so is applied to a low-substitution cellulose acylate film, then thefilm may be greatly stretched in the machine direction in the hightemperature and high humidity treatment step.

To that effect, the preferred range of the high temperature and highhumidity treatment temperature, the volumetric humidity and the relativehumidity in the case of using a low-substitution cellulose acylate isthe same as the preferred range in high temperature and high humiditytreatment of cellulose acylate having no specific limitation on thedegree of substitution therein.

The vapor (contact vapor) to be kept in contact with the celluloseacylate film in the high temperature and high humidity treatment step isa vapor containing water vapor, more preferably a vapor containing watervapor as the main ingredient thereof, even more preferably water vaporalone. The main ingredient of the vapor means that, when the vapor is asingle vapor, the main ingredient is the single vapor itself, and whenthe vapor is composed of multiple vapors, the main ingredient is thevapor having the highest mass fraction of all the constitutive vapors.

Preferably, the contact vapor is formed in a wet vapor supply apparatus.Concretely, a solvent in the form of a solution is heated with a boilerto be a vapor, which is then fed with a blower. The contact vapor may bemixed with air, and after fed with a blower, it may be heated via aheating unit. In this, the air is preferably heated. Thus formed, thetemperature of the contact vapor is preferably from 70 to 200° C., morepreferably from 80 to 160° C., most preferably from 100 to 140° C. Whenthe temperature is not higher than the uppermost limit, then it isfavorable since the film is not too much curled; and when not lower thanthe lowermost limit, the contact vapor produces a sufficient effect.

Preferably, the relative humidity of the contact vapor is from 10% to100%, more preferably from 15 to 100%, even more preferably from 20 to100%.

Regarding the contact method between the cellulose acylate film and theabove-mentioned contact vapor in the high temperature and high humiditytreatment step, employable is a method of applying the contact vapor tothe cellulose acylate film, a method of putting the cellulose acylatefilm in a space filled with the contact vapor, or a method of leadingthe film to pass through the space filled with the contact vapor. Ofthose, preferred is the method of applying the contact vapor to thecellulose acylate film, or the method of leading the film to passthrough the space filled with the contact vapor. Preferably, thecellulose acylate film is kept in contact with the contact vapor withthe film kept guided in the contact zone by zigzag-arranged pluralrollers therein.

The contact time with the contact vapor is not specifically defined.Within the range capable of attaining the effect of the invention, thecontact time is preferably as short as possible from the viewpoint ofthe production efficiency. The uppermost limit of the processing timeis, for example, preferably at most 60 minutes, more preferably at most10 minutes. On the other hand, the lowermost limit of the processingtime is, for example, preferably at least 10 seconds, more preferably atleast 30 seconds.

Not specifically defined, the temperature of the cellulose acylate filmbefore brought into contact with the contact time is preferably from 80to 130° C.

Not specifically defined, the residual solvent amount in the celluloseacylate film before the high temperature and high humidity treatment ispreferably such that the cellulose acylate molecules have almost lostthe flowability. Concretely, the residual solvent amount is preferablyfrom 0 to 5% by mass, more preferably from 0 to 0.3% by mass.

After kept in contact with the cellulose acylate film, the contact vaporis fed to a condensation unit connected with a cooling unit, in whichthe contact vapor may be separated into a hot vapor and a condensateliquid.

Regarding the timing of the high temperature and high humidity treatmentstep in the production method of the invention, the high temperature andhigh humidity treatment step may be just after the stretching step ormay be just after the drying step to be attained after the stretchingstep, or may also be after the step of once winding the film into a rollafter the stretching step. In case where the film is processed for thehigh temperature and high humidity treatment after it has been oncewound up into a roll, it may be processed directly as it is in the formof a roll, or after it is again unwound into a film.

(7) Drying Step after High Temperature and High Humidity Treatment:

The cellulose acylate film thus kept in contact with the contact vaporin the manner as above may be cooled to room temperature directly as itis, or for controlling the amount of the contact vapor moleculesremaining in the film, the film may be subsequently conveyed into adrying zone. In case where the film is conveyed into a drying zone,there may be employed a method where hot air or warm air or air having alow vapor concentration is applied to the cellulose acylate film keptconveyed with rolls or the cellulose acylate film kept conveyed withboth sides thereof clipped with a tenter, a method where the film isirradiated with heat rays, or a method where the film is kept in contactwith heated rolls. Preferred is the method of applying hot air or warmair or air having a low vapor concentration to the film. In case where awater vapor contact step is taken before the heat treatment step, theheat treatment step may be the drying step.

(8) Heat Treatment Step after High Temperature and High HumidityTreatment:

Preferably in the production method of the invention, the hightemperature and high humidity treatment step is followed by theabove-mentioned heat treatment step. In the invention, the heattreatment step may be attained after the high temperature and highhumidity treatment step and before the drying step; or after the hightemperature and high humidity treatment step, the drying step may servealso as the heat treatment step; or after the high temperature and highhumidity treatment step followed by the drying step, the film may beonce wound up and may be thereafter processed for heat treatment in theseparate step additionally provided in the method. Preferably in theinvention, the heat treatment step is provided after the hightemperature and high humidity treatment step and before the drying step.This is because the mode is advantageous in point of producing a filmhaving more excellent thermal dimensional stability.

The reason why the shrinkage of the film could be reduced through thetreatment is not clear, but it may be presumed that, in the filmstretched in the stretching step, the residual stress in the stretchingdirection is large and the residual stress is solved by the heattreatment whereby the contraction force of the film in the region nothigher than the heat treatment temperature could be thereby reduced.

The heat treatment may be attained according to a method of applying airat a predetermined temperature to the film being conveyed, or a methodof using a heating means such as microwaves, etc.

During drying by heat treatment, the volumetric humidity is preferably 0g/m³. Preferably, the heat treatment temperature in the heat treatmentstep is the same as the temperature in the high temperature and highhumidity treatment step from the viewpoint of preventing dewcondensation and preventing the film from shrinking.

In the heat treatment step, the film tends to shrink in the machinedirection or in the lateral direction. It is desirable that theshrinkage of the film is prevented as much as possible during the heattreatment for bettering the surface smoothness of the finished film. Forthis, preferably employed is a method of heat-treating the film withclipping or pinning both sides of the film in the lateral direction tothereby secure the width of the film (tenter mode). Also preferably, thefilm is elongated by from 0.9 times to 1.5 times in both the lateraldirection and the machine direction of the film.

(9) Winding Step:

For winding up the produced film, an ordinary winder may be used, andthe film may be wound up according to an ordinary winding method of aconstant tension method, a constant torque method, a taper tensionmethod or a programmed tension control method where the internal stressis kept constant. The film roll obtained in the manner as above ispreferably such that the slow axis direction of the film is at ±2degrees to the winding direction (machine direction of the film), morepreferably at ±1 degree. Also preferably, the slow axis direction of thefilm is at ±2 degrees to the direction perpendicular to the windingdirection (lateral direction of the film), more preferably at ±1 degree.Even more preferably, the slow axis direction of the film is at ±0.1degrees to the winding direction (machine direction of the film), or itis at ±0.1 degrees to the lateral direction of the film.

Regarding the length thereof, the film thus produced in the manner asabove is preferably wound up into a roll having a length of from 100 to10000 m, more preferably from 500 to 7000 m, even more preferably from1000 to 6000 m. The width of the film is preferably from 0.5 to 5.0 m,more preferably from 1.0 to 3.0 m, even more preferably from 1.0 to 2.5m. In winding up the film, preferably, the film is knurled at least onone side thereof, and the knurling width is preferably from 3 mm to 50mm, more preferably from 5 mm to 30 mm, and the knurling height ispreferably from 0.5 to 500 μm, more preferably from 1 to 200 μm. Theknurling may be in a mode of single pressing or double pressing.

The film of the invention is especially suitable for use in large-panelliquid crystal display devices. In case where the film is used as anoptical compensatory film for large-panel liquid crystal displaydevices, preferably, the film is shaped to have a film width of, forexample, at least 1470 mm. The optical compensatory film of theinvention includes not only an embodiment of a film sheet cut in a sizecapable of being directly incorporated in a liquid crystal displaydevice but also an embodiment of a film roll produced as a long film incontinuous production and wound up into a roll. The optical compensatoryfilm of the latter embodiment is stored and conveyed as it is, and whenit is in fact incorporated into a liquid crystal display device or whenit is stuck to a polarizing element or the like, it may be cut into asheet having a desired size. The film of the invention formed as a longfilm may be stuck, directly as it is, with a polarizing element formedof a polyvinyl alcohol film or the like similarly as a long film, andthereafter when the thus-stuck films are in fact incorporated in aliquid crystal display device, they may be cut into a desired size. Oneembodiment of the optical compensatory film wound up in the form of aroll may have a roll length of at least 2500 mm.

Thus produced, the film is wound up to give a final product, celluloseacylate film.

In the production method for the cellulose acylate film of theinvention, preferably, the thickness of the film is from 20 to 200 μm.When thinner than 20 μm, the mechanical strength of the film may be lowand the film may be broken or troubled in its production, and the filmsurface condition may be poor. The high temperature and high humiditytreatment effect is remarkable when the film thickness is within a rangeof from 20 to 200 μm. On the other hand, from the viewpoint of theproduction cost and the optical property appearance thereof, thecellulose acylate film is preferably so produced that its thicknesscould fall within the above-mentioned preferred range.

The film thickness may be controlled to be a desired one by controllingthe solid concentration in the dope, the slit gap of the die nozzle, theextrusion pressure from the die, the metal support speed, etc.

[Polarizer]

The polarizer of the invention contains a polarizing element and thefilm of the invention on at least one side of the polarizing element.The polarizer of the invention is described below.

Like the film of the invention, the polarizer of the invention alsoincludes not only an embodiment of a film sheet cut in a size capable ofbeing directly incorporated in a liquid crystal display device but alsoan embodiment of a film roll produced as a long film in continuousproduction and wound up into a roll (for example, an embodiment having aroll length of at least 2500 mm or at least 3900 mm). For use inlarge-panel liquid crystal display devices, the width of the polarizeris preferably at least 1470 mm, as so mentioned in the above.

For the concrete constitution of the polarizer of the invention, anyknown constitution is employable with no limitation thereon. Forexample, the constitution described in FIG. 6 in JP-A 2008-262161 may beemployed here.

[Liquid Crystal Display Device]

The liquid crystal display device of the invention contains at least onepolarizer of the invention.

The liquid crystal display device of the invention comprises a liquidcrystal cell and a pair of polarizers arranged on both sides of theliquid crystal cell, in which at least one polarizer is the polarizer ofthe invention. Preferably, the liquid crystal display device is an IPS,OCB or VA-mode liquid crystal display device.

The concrete constitution of the liquid crystal display device of theinvention is not specifically defined, and any known constitution isemployable therein. For example, one example of the constitution of theliquid crystal display device of the invention is shown in FIG. 1. Inaddition, the constitution described in FIG. 2 in JP-A 2008-262161 isalso employable here.

EXAMPLES

The present invention will be further specifically explained withreference to the following examples of the present invention. Thematerials, amounts, ratios, types and procedures of treatments and soforth shown in the following examples can be suitably changed unlesssuch changes depart from the gist of the present invention. Accordingly,the scope of the present invention should not be construed as limited tothe following specific examples.

<<Measurement Methods>>

In the invention, the samples were analyzed to measure their propertiesaccording to the following measurement methods.

(Optical Appearance)

Using KOBRA 21ADH (by Oji Scientific Instruments), Re and Rth of thesamples are measured at a wavelength of 450 nm, 550 nm and 630 nm,according to the method mentioned above. The measured Rth(550) isdivided by the film thickness d to give Rth(550)/d. Further,Re(630)−Re(450) is computed to give ΔRe, and the resulting ΔRe isdivided by Re(550) to give ΔRe/Re(550). The results are shown in Table 7below.

(Internal Haze)

A few drops of glycerin are applied onto both surfaces of the celluloseacylate film sample (having a size of 40 mm×80 mm) to be analyzed, thefilm is sandwiched between two glass plates (MICRO SLIDE GLASS Lot No.S9213, by Matsunami) each having a thickness of 1.3 mm, and at 25° C.and at a relative humidity of 60%, the haze value of the sample ismeasured with a haze meter (HGM-2DP, by Suga Test Instruments) accordingto JIS K-6714. On the other hand, a few drops of glycerin are putbetween two glass plates, and the haze value thereof is measured. Thelatter value is subtracted from the former value to give the internalhaze value (%) of the film sample. The results are shown in Table 7below.

(Dimensional Change)

The dimensional change before and after 24 hours at 60° C. and at arelative humidity of 90%, or that is, {(L′−L0)/L0}×100(%) is measured inthe machine direction and in the direction perpendicular thereto. Inthis, L0 means the length (unit: mm) of the film before aged for 24hours at 60° C. and at a relative humidity of 90%; and L′ means thelength (unit: mm) of the film after aged for 24 hours at 60° C. and at arelative humidity of 90% and further after conditioned for 2 hours. Thesample film has a size of 30 mm×120 mm, and the other condition is asmentioned below.

The film is conditioned in an atmosphere at 25° C. and at a relativehumidity of 60%, then using an automatic pin gauge (by ShintoScientific), 6 mmφ holes are formed at intervals of 100 mm to be inparallel to the 120-mm side of the film, and the original dimension ofthe distance (L0) is measured to the minimum scale, 1/1000 mm. Then,after aged for 24 hours at 60° C. and at a relative humidity of 90%, thefilm is conditioned in an atmosphere at 25° C. and at a relativehumidity of 60%, the dimension L′ of the distance between the holes ismeasured.

The results are shown in Table 7 below.

Examples 1 to 22, and Comparative Examples 1 to 7 (1) Preparation ofSynthetic Cellulose Acylate Resin

Cellulose acylates each having the degree of acyl substitution shown inTable 7 were prepared. As a catalyst, sulfuric acid (7.8 parts by massrelative to 100 parts by mass of cellulose) was added, and eachcarboxylic acid was added for acylation at 40° C. Subsequently, thetotal degree of substitution and the degree of 6-substitution werecontrolled by controlling the amount of the sulfuric acid catalyst, theamount of water and the aging time. The aging time was 40° C. Thecellulose acylate was washed with acetone to remove the low-molecularcomponent thereof.

(2) Preparation of Dope <1-1> Cellulose Acylate Solution

The following ingredients were put into a mixing tank and dissolved bystirring. The mixture was heated at 90° C. for about 10 minutes, andfiltered through paper filter having a mean pore size of 34 μm andthrough a sintered metal filter having a mean pore size of 10 μm.

a disperser to prepare a mat agent dispersion.

Cellulose Acylate Solution of Example 1 Cellulose Acylate shown in Table7 100.0 parts by mass in total below Sugar Ester shown in Table 7 below(amount shown in Table 7, unit: part by mass) Other Additive shown inTable 7 (amount shown in Table 7, below unit: part by mass) MethyleneChloride 403.0 parts by mass Methanol 60.2 parts by mass

In Table 7 below, Ac means an acetyl group, Pr means a propionyl group,Pht means a phthalyl group. The structure of each additive is shownbelow. Comparative Example 5 is the cellulose ester film No. 101 inExample in JP-A 2009-1696; and the acryl A in Table 7 is the acrylicpolymer A (main ingredient, polymethyl acrylate) described in the patentpublication.

TABLE 5 Sugar Ester Skeleton Acetyl Group Benzoyl Group 1 A 8 0 2 A 7 13 A 5 3 4 B 2 3 5 A 0 8 6 B 5 8 Skeleton A:

Skeleton B:

Compound (1): negative birefringent compound

Compound (2): negative birefringent compound

TABLE 6 Compound (3): Dicarboxylic Acids Number- Ratio of AverageAromatic Aliphatic Dicarboxylic Diol Molec- Dicarboxylic DicarboxylicAcids Aliphatic Termi- ular Acid Acid (by mol) Diol nal Weight PA/TPAAA/SA 10/50/30/10 ethane- Ac 800 diol residue Compound (4):

wherein one R is a methyl group and the other is a hydrogen atom.Compound (5):

<1-2> Mat Agent Dispersion:

Next, the following composition containing the cellulose acylatesolution prepared in the above was put into a disperser to prepare a matagent dispersion.

Mat Agent Dispersion Mat Agent (Aerosil R972) 0.2 parts by massMethylene Chloride 72.4 parts by mass Methanol 10.8 parts by massCellulose Acylate Solution 10.3 parts by mass

100 parts by mass of the cellulose acylate solution in Example 1 wasmixed with the mat agent dispersion in Example 1 in such a manner thatthe amount of the inorganic fine particles could be 0.02 parts by massof the cellulose acylate resin, thereby preparing a dope for filmformation.

(3) Casting

The dope was cast, using a band caster. The band was made of SUS.

(4) Drying

The web (film) obtained by casting was peeled from the band, and using atenter for conveying the web by clipping it at both sides thereof, theweb was dried in the tenter for 20 minutes. The drying temperature inthe process is the film surface temperature.

Tg (glass transition temperature) of the thus-obtained, unstretched filmwas determined according to the following method. The film sample havinga size of 5 mm×30 mm is conditioned at 25° C. and 60% RH for 2 hours ormore, then using a dynamic viscoelastometer DVA-25 (by IT KeisokuSeigyo), this is analyzed at a frequency of 1 Hz. The chuck-to-chuckdistance is 20 mm. The highest temperature at tan δ (=loss elasticmodulus (E″)/storage elastic modulus (E′)) is determined, and this is Tgof the film. The results are shown in Table 7 below.

(5) Stretching

The formed web (film) was peeled from the band, clipped, and stretchedunder the condition of side-fixed monoaxial stretching, in the directionperpendicular to the machine direction (lateral direction) at thestretching temperature and the draw ratio indicated in Table 7 below,while the residual solvent amount was from 30 to 5% relative to thetotal mass of the film, using a tenter.

Subsequently, the film was unclipped and dried at 110° C. for 30minutes. In this, the casting thickness was so controlled that thethickness (unit, μm) of the stretched film could be as in Table 7.

(6) High Temperature and High Humidity Treatment

The stretched film was processed for dew condensation preventiontreatment, high temperature and high humidity treatment (water vaporcontact treatment) and heat treatment in series.

In the dew condensation prevention treatment, dry air was applied to thefilm to control the film temperature (100° C.) Tf0.

In the high temperature and high humidity treatment (water vapor contacttreatment), the absolute humidity of the wet vapor (volumetric humidityin high temperature and high humidity treatment) inside the wet vaporcontact chamber was controlled to be the value as in Table 7, and thedew point of the wet vapor was so controlled as to be higher by at least10° C. than the film temperature Tf0. While the film temperature (hightemperature and high humidity treatment temperature) as shown in Table 7was kept for the processing time (60 seconds), the film was conveyedthrough the chamber.

(7) Drying and (8) Heat Treatment after High Temperature and HighHumidity Treatment

In the heat treatment, the absolute humidity of the vapor in the heattreatment chamber (volumetric humidity in heat treatment) was 0 g/m³,and the temperature of the film (heat treatment temperature) was set tobe the same temperature as the high temperature and high humiditytreatment temperature, and the film was kept as such for the processingtime (2 minutes). The film surface temperature was measured withtape-type thermocouple surface temperature sensors (Anritsu Meter's STSeries) stuck to three points of the film surface, and the data of thesensors were averaged.

(9) Winding

Subsequently, the film was cooled to room temperature and wound up. Forthe purpose of determining the production aptitude of the film, at least24 rolls of the film each having a roll width of 1280 mm and a rolllength of 2600 mm were produced under the condition as above. Of those24 rolls continuously produced, one roll was sampled at intervals of 100m to give samples each having a length of 1 m (width of 1280 mm), andthese were analyzed as films of Examples and Comparative Examples.

TABLE 7 Production Method High temperature Dope Composition and highhumidity Sugar Ester Stretching Treatment Film Properties CelluloseAcylate Compound Other Additive tem- tem- volu- Un- Film Retardation In-Dimensional mas. mas. mas. mas. per- draw per- metric stretched Thick-Re Rth ternal Change pts. pts. pts. pts. ature ratio ature humidity Tgness (550) (550) Rth(550)/ ΔRe ΔRe/ Haze TD MD type [%] type [%] type[%] type [%] [° C.] [%] [° C.] [g/m³] [° C.] [μm] [nm] [nm] d × 10⁻³[nm] Re(550) [%] [%] [%] Example 1 Ac 2.43 100 — — 1 15 — — 170 45 100300 190 65 50 115 1.8 8 0.17 0.05 0.1 0.3 Example 2 Ac 2.43 100 — — 4 15— — 170 45 100 300 190 65 55 127 1.9 7 0.12 0.06 0.1 0.4 Example 3 Ac2.43 100 — — 1 10 compound (1) 5 170 45 100 300 190 65 48 109 1.7 110.23 0.07 0.1 0.2 Example 4 Ac 2.43 100 — — 1 10 compound (2) 5 170 45100 300 190 65 45 104 1.6 13 0.28 0.07 0.1 0.3 Example 5 Ac 2.43 100 — —1 10 acrylic A 5 170 45 100 300 190 65 49 113 1.7 9 0.19 0.07 0.1 0.2Example 6 Ac 2.43 100 — — 4 10 compound (1) 5 170 45 100 300 190 65 52120 1.8 9 0.17 0.06 0.1 0.3 Example 7 Ac 2.30 100 — — 1 15 — — 170 45100 300 190 46 53 121 2.7 6 0.11 0.05 0.1 0.4 Example 8 Ac 2.50 100 — —1 15 — — 170 45 100 300 189 46 48 109 2.4 11 0.23 0.05 0.1 0.3 Example 9Ac 2.43 100 — — 2 15 — — 170 45 100 300 190 65 53 121 1.9 8 0.15 0.050.1 0.3 Example 10 Ac 2.43 100 — — 3 15 — — 170 45 100 300 190 65 55 1271.9 8 0.14 0.06 0.1 0.3 Example 11 Ac 2.43 100 — — 3 15 — — 170 45 100300 190 65 48 109 1.7 8 0.17 0.05 0.1 0.2 Example 12 Ac 2.43 100 — — 120 — — 160 45 100 300 180 65 52 118 1.8 8 0.16 0.05 0.1 0.3 Example 13Ac 2.43 100 — — 4 20 — — 160 45 100 300 180 65 58 132 2 7 0.13 0.05 0.10.3 Example 14 Ac 2.43 100 — — 1 15 — — 175 45 80 300 180 78 51 117 1.58 0.16 0.04 0.1 0.3 Example 15 Ac 2.43 100 — — 1 15 — — 160 45 120 300180 52 49 113 2.2 9 0.18 0.06 0.1 0.3 Example 16 Ac 1.7  100 — — 1 10 —— 155 30 100 300 175 55 50 138 2.5 6 0.11 0.05 −0.1 −0.15 Pr 0.9 Example17 Ac 2.20 100 — — 1 5 — — 160 50 100 300 190 25 45 115 4.6 5 0.11 0.040.1 0.3 Example 18 Ac 2.20 100 — — 1 10 — — 155 55 100 300 190 22 47 1135.1 5 0.11 0.05 0.1 0.2 Example 19 Ac 2.43 100 — — 1 13 — 0 160 30 100300 190 49 50 120 2.4 8 0.16 0.03 −0.3 −0.1 Example 20 Ac 2.43 100 — — 113 compound (4) 2 160 30 100 300 186 50 51 119 2.4 6 0.12 0.02 −0.2 0.0Example 21 Ac 2.43 100 — — 6 13 compound (4) 2 160 30 100 300 172 52 50115 2.2 6 0.12 0.01 −0.1 −0.1 Example 22 Ac 2.43 100 — — 6 13 compound(5) 2 160 30 100 300 172 52 50 115 2.2 6 0.12 0.01 −0.1 −0.1 ComparativeAc 2.43 100 — — 1 15 — — 170 45 — — 190 65 51 117 1.8 8 0.17 0.05 0.30.9 Example 1 Comparative Ac 2.43 100 — — 1 15 — — 170 45 150 500 190 6535 81 1.2 6 0.17 0.10 0.1 0.3 Example 2 Comparative Ac 2.43 100 — — 1 15— — 170 45 70 140 190 65 43 98 1.5 7 0.17 0.08 0.2 0.6 Example 3Comparative Ac 2.43 100 — — 1 15 — — 170 45 40 dipped 190 65 51 116 1.88 0.17 0.05 0.3 0.8 Example 4 in water Comparative Ac 2.43 100 — — 1 15— — 190 45 — — 190 65 40 91 1.4 7 0.17 0.04 0.1 0.4 Example 5Comparative Ac 2.43 100 — — — — compound (3) 15  180 45 100 300 190 6555 115 1.8 8 0.15 0.20 0.1 0.4 Example 6 Comparative Ac 2.4   50 Ac 1.650 5 10 acrylic A 3 170 45 — — 180 65 78 169 2.6 5 0.07 0.04 0.1 0.1Example 7 Pht 0.5 Pr 0.9

From Table 7, it is known that the films of Examples all have highoptical appearance and exhibit strong reversed wavelength dispersioncharacteristics, and their haze is small and their dimensional change inhigh temperature and high humidity environments is small.

On the other hand, it is known that the dimensional change in hightemperature and high humidity environments of the film of ComparativeExample 1 not processed for high temperature and high humidity treatmentis great. It is also known that, for the film of Comparative Example 5similarly not processed for high temperature and high humiditytreatment, even when the stretching temperature is optimized in thedirection of improving only the dimensional stability of the film, theoptical appearance of the film is still insufficient. It is known that,for the film of Comparative Example 7 similarly not processed for hightemperature and high humidity treatment, even when the type of thecellulose acylate is optimized in the direction of improving only thedimensional stability of the film, the optical appearance of the film istoo great and therefore the film could not be controlled within thepreferred range thereof for use for liquid crystal display devices. Itis known that the film of Comparative Example 2, which was processed forhigh temperature and high humidity treatment under the high temperatureand high humidity treatment condition overstepping the scope of theproduction method of the invention toward the side of high temperatureand high volumetric humidity condition, is unsatisfactory in point ofthe optical appearance thereof. It is known that the film of ComparativeExample 3, which was processed for high temperature and high humiditytreatment under the high temperature and high humidity treatmentcondition overstepping the scope of the production method of theinvention toward the side of low temperature and low volumetric humiditycondition, is unsatisfactory in point of the optical appearance thereof,and in addition, the dimensional change of the film under hightemperature and high humidity environments is great. It is known thatthe film of Comparative Example 6 not containing a sugar ester compoundhas a large internal haze.

(Production of Polarizer Sample)

The surface of the film produced in the above-mentioned Examples andComparative Examples was alkali-saponified. Briefly, the film was dippedin an aqueous solution of sodium hydroxide 1.5 N at 55° C. for 2minutes, then washed in a water-washing bath at room temperature, andneutralized with 0.1 sulfuric acid at 30° C. Again this was ashed in awater-washing bath at room temperature, and then dried with hot air at100° C. Subsequently, a roll of polyvinyl alcohol film having athickness of 80 μm was unrolled and continuously stretched by 5 times inan aqueous iodine solution and dried to give a polarizing element havinga thickness of 20 μm. Using a 3% aqueous solution of polyvinyl alcohol(Kuraray's PVA-117H) as an adhesive, the alkali-saponified film ofExamples and Comparative Examples was stuck to Fujitac TD80UL (byFUJIFILM) that had been alkali-saponified like in the above, with thepolarizing element sandwiched therebetween in such as manner that thesaponified surfaces of the two films could face the polarizing elementside, thereby producing a polarizer in which the film of Examples andComparative examples, the polarizing element, TD80UL were stuck togetherin that order. The polarizing element and the films were so arrangedthat the MD direction of the film of Examples and Comparative examplesand the slow axis of TD80UL could be parallel to the absorption axis ofthe polarizing element.

(Production of Liquid Crystal Display Device)

The polarizers and the retardation films on the front side and therear-side of a VA-mode liquid crystal TV (LC-46LX1, by Sharp) werepeeled away from the device to prepare a liquid crystal cell for useherein. As in FIG. 1 (in this, the upper side is the front side), anouter protective film (not shown), a polarizing element 11, a film 14 ofExamples and Comparative Examples shown in Table below (rear-sidecellulose acylate film), a liquid crystal cell 13 (the above-mentionedVA liquid crystal cell), a film 15 of Examples and Comparative Examplesshown in Table below (front-side cellulose acylate film), a polarizingelement 12 and an outer protective film (not shown) were stuck togetherwith an adhesive in that order, thereby producing a liquid crystaldisplay device of Examples and Comparative Examples. In this, thepolarizers were so arranged that the absorption axis of the upper andlower polarizers could be perpendicular to each other.

(Front Contrast)

Using a measuring instrument (BM5A, by TOPCON), the brightness of thedisplay device was measured in a dark room at the time of black stateand white state in the panel normal direction, and the front contrast(white-state brightness/black-state brightness) of the device wascomputed from the found data.

The results are shown in Table 8 below.

(Viewing Angle Contrast)

Using a measuring instrument (BM5A, by TOPCON), the brightness of thedisplay device was measured in a dark room at the time of black stateand white state in an oblique direction of 45° to the panel, and thefront contrast (white-state brightness/black-state brightness) of thedevice was computed from the found data.

The results are shown in Table 8 below.

(Color Shift)

For display performance evaluation of the liquid crystal display device,the color shift (Δu′v′) was determined under the condition mentionedbelow.

Using a measuring instrument (BM5A, by TOPCON), the brightness of thedisplay device was measured in a dark room at the time of black state inthe panel normal direction. The display device was fixed at a polarangle of 45°, and the visual field thereof was varied from 0 to 360° ofthe azimuth angle whereupon the color shift Δu′v′ was determined as theindex according to the following formula. The results are shown in Table8 below.

Δu′v′={((u′(maximum value)−u′(minimum value))²+((v′(maximumvalue)−v′(minimum value))²}^(0.5)

Preferably, the color shift Δu′v′ is at most 0.06; and for practicaluse, the color shift is desired to be at most 0.05, more preferably atmost 0.04.

(Corner Unevenness)

For display performance evaluation of the liquid crystal display device,the corner unevenness was determined under the condition mentionedbelow.

The produced liquid crystal display device was left at 60° C. and at arelative humidity of 90% for 240 hours, then conditioned at 25° C. andat a relative humidity of 60% for 24 hours, and the display device wasvisually checked for corner unevenness at the time of black state.

Thus observed, the corner unevenness level was evaluated according tothe following criteria:

◯: Good.

Δ: Some corner unevenness found.x: Extreme corner unevenness found.

The results are shown in Table 8 below.

TABLE 8 Viewing Angle CR Color Corner (obliquely Shift Unevenness FrontCR at 45°) (Δu′v′) Level Example 1 3980 113 0.04 ∘ Example 2 3960 490.05 ∘ Example 3 3940 113 0.03 ∘ Example 4 3940 68 0.02 ∘ Example 5 3940113 0.04 ∘ Example 6 3960 85 0.04 ∘ Example 7 3989 86 0.05 ∘ Example 83989 95 0.03 ∘ Example 9 3982 86 0.05 ∘ Example 10 3975 63 0.05 ∘Example 11 3989 95 0.04 ∘ Example 12 3989 94 0.05 ∘ Example 13 3989 450.05 ∘ Example 14 4017 97 0.04 ∘ Example 15 3975 101 0.04 ∘ Example 174017 113 0.06 ∘ Example 18 3989 101 0.06 ∘ Example 19 4017 85 0.04 ∘Example 20 4074 92 0.05 ∘ Example 21 4103 113 0.05 ∘ Example 22 4103 1130.05 ∘ Comparative 3980 97 0.04 x Example 1 Comparative 3800 23 0.04 ∘Example 2 Comparative 3648 52 0.06 Δ Example 3 Comparative 3648 99 0.06x Example 4 Comparative 4200 34 0.04 ∘ Example 5 Comparative 3600 1130.05 ∘ Example 6 Comparative 4000 8 0.06 ∘ Example 7

The liquid crystal display device of Example 16 was evaluated in thesame manner as above, and gained the same results as those of the otherExamples in the above Table 8.

From the above, it is known that the liquid crystal display devices ofExamples are all good in point of the front contrast, the viewing anglecontrast, the color shift and the corner unevenness level.

On the other hand, it is known that, when the film of ComparativeExample 1 having a large dimensional change in wet environments is used,then the corner unevenness level of the liquid crystal display device ishigh. It is known that, when the films of Comparative Examples 2 and 5having poor optical appearance are used, then the liquid crystal displaydevices are not good in point of the viewing angle contrast. It is knownthat, when the films of Comparative Examples 3 and 4 having a largedimensional change in the MD direction in wet environments are used,then the front contrast is small, the color shift is large and thecorner unevenness level is high. It is known that when the film ofComparative Example 6 having a large internal haze is used, then thefront contrast is small. It is known that, when the film of ComparativeExample 7 of which the retardation is too large is used, then theviewing angle contrast is small and the color shift is large.

While the present invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

The present disclosure relates to the subject matter contained inJapanese Patent Application No. 2010-96470, filed on Apr. 19, 2010;Japanese Patent Application No. 2010-188438, filed on Aug. 25, 2010; andJapanese Patent Application No. 2011-51796, filed on Mar. 9, 2011, thecontents of which are expressly incorporated herein by reference intheir entirety. All the publications referred to in the presentspecification are also expressly incorporated herein by reference intheir entirety.

The foregoing description of preferred embodiments of the invention hasbeen presented for purposes of illustration and description, and is notintended to be exhaustive or to limit the invention to the precise formdisclosed. The description was selected to best explain the principlesof the invention and their practical application to enable othersskilled in the art to best utilize the invention in various embodimentsand various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention not belimited by the specification, but be defined claims set forth below.

1. A cellulose acylate film comprising: a cellulose acylate and a sugarester compound, wherein the sugar ester comprises from 1 to 12 pyranosestructures or furanose structures in which at least one hydroxyl groupis esterified, wherein the film has an in-plane retardation at awavelength of 550 nm satisfying the following formula (1):40 nm≦Re(550)≦60 nm  (1) wherein RE(550) means the in-plane retardationof the film at a wavelength of 550 nm, wherein the film has athickness-direction retardation at a wavelength of 550 nm satisfying thefollowing formula (2):100 nm≦Rth(550)≦140 nm  (2) wherein Rth(550) means thethickness-direction retardation of the film at a wavelength of 550 nm,the film has a dimensional change before and after 24 hours at 60° C.and at a relative humidity of 90% satisfying the following formula (3)in the film conveying direction and in the direction perpendicularthereto,−0.5%≦{(L′−L0)/L0}×100≦0.5%  (3) wherein L0 means the length (unit: mm)of the film before aged for 24 hours at 60° C. and at a relativehumidity of 90%; and L′ means the length (unit: mm) of the film afteraged for 24 hours at 60° C. and at a relative humidity of 90% andfurther after conditioned for 2 hours, and wherein the film has aninternal haze of at most 0.1%.
 2. The cellulose acylate film accordingto claim 1, satisfying the following formula (4):0.02≦ΔRe/Re(550)≦0.28  (4)ΔRe=Re(630)−Re(450)  (4′) wherein Re(630) means the in-plane retardationof the film at a wavelength of 630 nm; Re (450) means the in-planeretardation of the film at a wavelength of 450 nm; Re(550) means thein-plane retardation of the film at a wavelength of 550 nm.
 3. Thecellulose acylate film according to claim 1, satisfying the followingformula (5):0.11≦ΔRe/Re(550)≦0.23  (5)ΔRe=Re(630)−Re(450)  (5′) wherein Re(630) means the in-plane retardationof the film at a wavelength of 630 nm; Re (450) means the in-planeretardation of the film at a wavelength of 450 nm; Re(550) means thein-plane retardation of the film at a wavelength of 550 nm.
 4. Thecellulose acylate film according to claim 1, wherein the degree of acylsubstitution of the cellulose acylate is from 2.0 to 2.6.
 5. Thecellulose acylate film according to claim 1, wherein the celluloseacylate is a cellulose acetate.
 6. The cellulose acylate film accordingto claim 1, comprising an additive having a negative intrinsicbirefringence.
 7. The cellulose acylate film according to claim 1,satisfying the following formula (6):1.5×10⁻³ <Rth(550)/d  (6) wherein Rth(550) means the thickness-directionretardation (unit: nm) of the film at a wavelength of 550 nm, and dmeans the thickness (unit: mm) of the film.
 8. The cellulose acylatefilm according to claim 1, having a thickness of from 40 to 80 μm. 9.The cellulose acylate film according to claim 1, comprising anitrogen-containing aromatic compound-type plasticizer.
 10. A method forproducing a cellulose acylate film, comprising: forming a polymersolution that comprises a cellulose acylate and a sugar ester compoundcomprising from 1 to 12 pyranose structures or furanose structures inwhich at least one hydroxyl group is esterified, into a film, stretchingthe film, and processing the stretched film in high temperature and highhumidity environments under a condition satisfying the followingformulae (7) and (8):70° C.≦temperature of the treatment≦140° C.  (7)250 g/m³≦volumetric humidity of the treatment≦400 g/m³  (8)
 11. Themethod for producing a cellulose acylate film according to claim 10,wherein the film is stretched at a temperature not higher than (Tg−5°C.) in which Tg means the glass transition temperature (unit: ° C.) ofthe unstretched cellulose acylate film.
 12. The method for producing acellulose acylate film according to claim 10, wherein the celluloseacylate has a degree of acyl substitution of from 2.0 to 2.6.
 13. Themethod for producing a cellulose acylate film according to claim 10,wherein the cellulose acylate is a cellulose acetate.
 14. The method forproducing a cellulose acylate film according to claim 10, wherein thepolymer solution comprises an additive having a negative intrinsicbirefringence.
 15. The method for producing a cellulose acylate filmaccording to claim 10, wherein the polymer solution comprises anitrogen-containing aromatic compound-type plasticizer.
 16. A celluloseacylate film produced by the method for producing a cellulose acylatefilm of comprising: forming a polymer solution that comprises acellulose acylate and a sugar ester compound comprising from 1 to 12pyranose structures or furanose structures in which at least onehydroxyl group is esterified, into a film, stretching the film, andprocessing the stretched film in high temperature and high humidityenvironments under a condition satisfying the following formulae (7) and(8):70° C.≦temperature of the treatment≦140° C.  (7)250 g/m³≦volumetric humidity of the treatment≦400 g/m³  (8)
 17. Apolarizer comprising a polarizing element and the cellulose acylate filmcomprising: a cellulose acylate and a sugar ester compound, wherein thesugar ester comprises from 1 to 12 pyranose structures or furanosestructures in which at east one hydroxyl group is esterified, whereinthe film has an in-plane retardation at a wavelength of 550 nmsatisfying the following formula (1):40 nm≦Re(550)≦60 nm  (1) wherein RE(550) means the in-plane retardationof the film at a wavelength of 550 nm, wherein the film has athickness-direction retardation at a wavelength of 550 nm satisfying thefollowing formula (2):100 nm≦Rth(550)≦140 nm  (2) wherein Rth(550) means thethickness-direction retardation of the film at a wavelength of 550 nm,the film has a dimensional change before and after 24 hours at 60° C.and at a relative humidity of 90% satisfying the following formula (3)in the film conveying direction and in the direction perpendicularthereto,−0.5%≦{(L′−L0))/L0}×100≦0.5%  (3) wherein L0 means the length (unit: mm)of the film before aged for 24 hours at 60° C. and at a relativehumidity of 90%; and L′ means the length (units: mm) of the film afteraged for 24 hours at 60° C. and at a relative humidity 90% and furtherafter conditioned for 2 hours, and wherein the film has an internal hazeof at most 0.1% on at least one side of the polarizing element.
 18. Aliquid crystal display device comprising a polarizing element and thecellulose acylate film comprising a cellulose acylate and a sugar estercompound wherein the sugar ester comprises from 1 to 12 pyranosestructures or furanose structures in which at least one hydroxyl groupis esterified, wherein the film has an in-plane retardation at awavelength of 550 nm satisfying the following formula (1):40 nm≦Re(550)≦60 nm  (1) wherein RE(550) means the in-plane retardationof the film at a wavelength of 550 nm, wherein the film has athickness-direction retardation at a wavelength of 550 nm satisfying thefollowing formula (2):100 nm≦Rth(550)≦140 nm  (2) wherein Rth(550) means thethickness-direction retardation of the film at a wavelength of 550 nm,the film has a dimensional change before and after 24 hours at 60° C.and at a relative humidity of 90% satisfying the following formula (3)in the film conveying direction and in the direction perpendicularthereto,−0.5%≦{(L′−L0)/L0}×100≦0.5%  (3) wherein L0 means the length (unit: mm)of the film before aged for 24 hours at 60° C. and at a relativehumidity of 90%; and L′ means the length (unit: mm) of the film afteraged for 24 hours at 60° C. and at a relative humidity of 90% andfurther after conditioned for 2 hours, and wherein the film has aninternal haze of at most 0.1% on at least one side of the polarizingelement.